2, 2-Diphenyl-1-picryldydrazyl (DPPH.), ascorbic acid, were procured from Sigma–Aldrich (St. Louis, MO, USA). Standard drugs Diclofenac sodium, Albendazole, Glibenclamide, Warfarin; and Vincristine sulfate were obtained from Square Pharmaceuticals Ltd. and Beacon Pharmaceuticals Ltd. Bangladesh, respectively. All other chemicals were reagent grades. Swiss albino mice of ages 6-7 weeks and weight 22-28g were collected from Jahangirnagar University, Bangladesh. They were adapted for the experimental environment maintained at suitable conditions (55-65% relative humidity, 27 ± 1 0C temperature, and 12:12 h light-dark cycle for two weeks). The leaves of Ceriops decandra and Ceriops tagal were collected from the Sundarbans, Bangladesh. The plant samples were authenticated by experts in Bangladesh National Herbarium, Mirpur, Dhaka, (Accession No.: DACB- 43819 and DACB- 43823, respectively) where voucher specimens have been deposited as reference. The collected leaves were detached from undesirable materials, washed with distilled water and dried under shade, and finally ground into a coarse powder using a suitable grinder (Capacitor start the motor, Wuhu motor factory, China). About 450 g ground powders were macerated in 1000 ml of ethanol (95%) for 14days accompanying routine shaking and stirring. The yield was obtained as 3.16% and 4.55% for C. decandra and C. tagal, respectively followed by filtration and evaporation of the solvent. Then the crude extracts were fractionated using n-hexane, ethyl acetate, butanol, and water. And finally, 0.85 g, 2.47 g, 2.06 g, 3.17 g extract were obtained for n-hexane, ethyl acetate, butanol, and water fraction for C. decandra and 0.92 g, 2.35 g, 1.96 g, 3.25 g for C. tagal leaves extract. Diverse phytochemical groups such as tannins alkaloids reducing sugar, combined reducing sugar, xanthoprotein, saponins, gum, steroids, glycosides, flavonoids terpenoids and acidic compounds were identified by characteristic visual/physical change applying standard chemical tests procedure [20]. Folin-Ciocalteu’s method was used with minor modifications for determining the total phenolic content of the test extracts [21]. Briefly, test sample (1 mg/mL) was mixed with 5 mL of 10% (v/v) Folin-Ciocalteu reagent and 4 mL of sodium carbonate (75 g/L). The reaction mixture was left at 40 °C for 30 mins. After that, the absorbance of the reaction mixture was taken at 765 nm in a UV spectrophotometer. A standard calibration curve of gallic acid for different concentrations (0.1–0.5 mg/ mL) was prepared from where total phenol content was determined (unit: mg gallic acid equivalent (GAE) per gram of dry extract). Aluminum chloride colorimetric assay was applied for estimating total flavonoid content. In 1 ml of the extract solution (1 mg/mL), 4 mL of distilled water and 0.3 mL NaNO2 (5% w/v) were added. Five minutes later, 0.3 mL AlCl3 (10% w/v) and 2 mL NaOH (1M) were added and adjusted the volume up to 10 mL. Then it was kept for 15 minutes at room temperature and absorbance was recorded at 510 nm. Here, a standard calibration curve was prepared using quercetin (0.25-1 mg/mL) and the total flavonoid content of the extract was expressed in mg quercetin equivalent (QE)/g of dried extract. The Folin Ciocalteu method was used here to determine the tannin content of the extracts [23]. In 0.1 ml of the extract solution, 7.5 mL of distilled water and 0.5 mL of Folin Ciocalteu phenol reagent, 1 mL of 35% (w/v) Na2CO3 solution was added and diluted up to 10 mL adding distilled water. After thorough mixing by proper shaking, the reaction mixture was stored at room temperature for half an hour. A calibration curve was prepared using tannic acids solutions as standard (20-100 μg/mL). Absorbance was taken for both samples and standard solutions at 725 nm and the resultant tannin content was recorded as mg of TAE /g of the dry extract. This test was performed following the Meyer method [31, 32] where Brine shrimp nauplii hatched from Artemia salina leach eggs were used as the test organism. Simulated seawater was used as the hatching medium with a constant oxygen supply and two days were required for complete hatching to matured nauplii. At first, the extracts (50 mg) were dissolved in dimethylsulfoxide (DMSO) and solutions of different concentrations (640, 320, 160, 80, 10, 40, 20µg/mL) were prepared using simulated seawater. Every time it was ensured that the concentration of DMSO in these test tubes did not exceed 10μl/ml. The solutions were then transferred to the pre-marked vials having 10 live brine shrimps nauplii in 5 mL simulated seawater. After 24 h interval, the number of living nauplii in each vial was counted was visually inspected and the percent of the lethality of the brine shrimp nauplii was calculated. The median lethal concentration LC50 of the test samples after 24 hr was obtained by a plot of the percentage of the shrimps died against the sample concentration (toxicant concentration) and the best fit line was obtained from the curve data using regression analysis. In this assay, vincristine sulfate served as the standard.