Fungal Phytase: The current experiment was conducted at faculty of veterinary medicine of University Putra Malaysia, Malaysia. The commercially produced fungal phytase (Natuphos®5000) synthesized from Aspergillus niger was pioneered by BASF, The Chemical Company, Germany. Birds, Feeding and Management: In this research, a total number of 72, one-day-old male broiler chicks (Cobb strain) of nearly similar live body weight were obtained from a commercial hatchery. The birds were housed in an environmentally controlled automatic climatic chamber for seven weeks with continuous lighting and controlled ventilation. The temperature was maintained at 30-320C for the first week and then gradually reduced according to normal management practices until a temperature of at around 250C which was maintained during the remaining period. The chicks were randomly assigned to one control and one experimental groups comprising three replicates of twelve birds each, and were placed in separate cages. There were fed a basal diet grouped T0 (control) and the basal diet supplemented with 1500 FTU kg-1of diet grouped as T1. The phytase enzyme (Natuphos®5000) was added just prior to give feed to chicks at a day. The basal diet was formulated to cover nutrient requirements of broiler chicks as recommended by NRC (1994). The ingredients and calculated analysis of the experimental basal diets are shown. Feed in a dry mash form and fresh water were offered ad libitum basis consumption throughout the experimental period. Vaccines of ND ‘V4 HR’ for ND was obtained from Malaysian Vaccines and Pharmaceuticals Sdn. Bhd (Co. No. 82381-X), Kuala Lumpur, Malaysia, and vaccination schedules were followed according to the manufacturer’s instructions. Sampling and Measurement: Initial bodyweight of each chick was recorded on replicate basis at arrival. At every week interval, before giving feed two birds from each treatment per replicate were picked up randomly and were then tagged numerically on their convenient place (legs &/or wings). For evaluation of growth performance at weekly, lives body weight gains were weighted by digital balance and recorded from the selecting birds. The birds were then slaughtered to obtain blood for serum preparation to determine specific antibodies (Ab), IgM, as well as IgG and mucosal fluid to quantify IgA. Roughly, 3 ml of blood was directly collected from each slaughtering bird into a Vacationer tube without anticoagulant and serum was prepared according to method described by Bush (1975). Jejunal mucosa was used to prepare mucosal fluid, immediately after blood collection from the slaughtering birds. The procedures were followed according to the method described by Liu et al., 2008. At the end of the experiment when the birds were of six week old, blood samples were collected for measurement of complete hemogram, and blood biochemical constituents. Usually, around 4 ml of blood was directly aliquoted from the selecting birds into collecting tubes with lithium heparin as an anticoagulant. Each sample was put in its own labeled tube. After estimation of complete hemogram, the remaining blood was then centrifuged at 5000 rpm for 10 minutes. The plasma was later separated into a microtube and stored at -200C until measurement of biochemical constituents. IDEXX FlockChek* NDV (IDEXX Laboratories, USA) was used for the detection of Ab to NDV in chicken serum, and the procedures were followed according to the manufacturer’s instructions.Chicken IgM ELISA Quantitation Set, Chicken IgA ELISA Quantitation Set, and Chicken IgG ELISA Quantitation Set (Bethyl Laboratories, Inc., USA) were used to determine the non-specific IgM, IgA, and IgG in chicken serum, respectively.The values of red blood cell (RBC), white blood cell (WBC), platelet (PLT) count, hemoglobin (Hb), mean corpuscular volume (MCV) and mean corpuscular Hb concentration (MCHC) were determined by an automated hematology analyzer (Abbott CELL-DYN 3700 Hematology Analyzer, GMI) using commercial reagents and other values (packed cell volume, heterophil, eosinophil, basophil, lymphocyte, monocyte, icterus index and total plasma protein) were determined manually.Using a chemistry analyzer (HITACHI 902, Japan), the technical procedures of test methods were described to measure blood biochemical constituents in broiler chickens. The constituents, such as albumin (Alb), total protein (TP), alanine transaminase (ALT), alkaline phosphatase (ALP), aspartate transaminase (AST), gamma-glutamyl transpeptidase (GGT), lactate dehydrogenase (LDH), cholesterol (Chol), triglyceride (Trig), Glucose (Glu), calcium (Ca), phosphorus, urea, creatinine (Creat), and uric acid (UA) were determined by colorimetry (absorbance measurement) method using available commercial kits. The parameters of sodium (Na), potassium (K), and Chloride (Cl) were determined by the ion-selective electrode method. Statistical Analysis: All the experiments were conducted using a completely randomized design (CRD) with three replications. The data were subjected to analysis of variance (ANOVA) and tested for significance using the least significant difference (LSD) by PC-SAS software (SAS Institute, 2009). Differences were considered significant at P≤0.05.