The experiment was carried out in the laboratory designed for research on "Azolla and blue-green algae". Azalia pinnata R. Br. mosquito Fern, water velvet (English), it is an aquatic plant can spread rapidly, and has the ability to survive on moist soil in and around rivers, ditches, and ponds. It forms dense surface mats, which degrade water quality by reducing oxygen levels, and can interfere with boating, fishing and recreational activities. Azolla is useful as a "soybean plant in rice field", because it can assimilate atmospheric nitrogen gas owing to the nitrogen fixation by cyanobacteria (blue green algae) living in the cavities located at the lower side of upper (dorsal) lobes of leaf. Blue-green algae (BGA), technically known as cyanobacteria, are microscopic organisms that are naturally present in lakes and streams. They usually are present in low numbers. Blue-green algae can become very abundant in warm, shallow, undisturbed surface water that receives a lot of sunlight. All BGA are prokaryotic, i.e. they lack true nucleus, nucleolus and nuclear membrane in their cells. They also lack plastids, flagella, and the sexual mode of reproduction. But somatic fusion of nuclear materials, a kind of genetic recombination known as parasexuality is present in some species. The symbiotic association of the algae aids in the creation of a huge amount of biomass on the surface of the water. It is then harvested, dried and used as biofertilizer to supplement the needs of nitrogen in coffee farms. Some experimental studies with the BGA in Bangladesh have many characteristic features similar to true bacteria and for this reason these are now classified by many with the bacteria and are called cyanobacteria. One of the bacterial features is fixation of the atmospheric nitrogen to soil and water, particularly in tropical countries. This N2-fixation ability of the BGA was first proved experimentally and conclusively by Dr PK De of the University of Dhaka in 1939 with the soil BGA collected from Faridpur rice- fields. Agriculturally, this information is very important and nowaday various BGA are used as biofertilisers to improve soil-fertility in tropical Asia, Africa and Latin American countries. The most commonly used pesticide Furadan 5G was used for the study. For the experiment blue-green algae were isolated from saline soil, calcareous soil and red soil of Bangladesh. Three different types of paddy soils viz. saline soil, calcareous soil and red soil were selected for the study. For each type of soil three locations were considered and there were nine locations in total under study. The selected areas were located in three administrative divisions namely Khulna, Rajshahi and Dhaka comprising four Agro-ecological Zones (AEZ) and four general soil types of Bangladesh. Locations, AEZ and General Soil Types under study have been presented. Soil samples were collected from the rice fields of the selected areas from 0-15 cm depth. After collection the soils samples were divided into equal halves, one for physicochemical analyses and other for Microbiological studies. The soil samples were made free form roots and gravels. For physicochemical analyses of soils, composite samples were air dried ground and passed through 10 mesh sieve. Different parameters such as Soil texture, pH, Organic matter content, Total nitrogen, Available Phosphorus, Available Sulfur, Electrical Conductivity (EC), Exchangeable potassium, calcium and sodium, Cation exchange capacity (CEC) etc. were analyzed from the soil samples using standard methods like., Hydrometer method for soil texture, wet oxidation methods for organic matter contents, Kjeldahl digestion method for total nitrogen contents etc. For microbial study different standard methods like; blue green algae broth and agar media, and soil-water media were followed such as preparation of media, preparation of dilution series, inoculation, isolation and identification of BGA, preparation of agar plates, preparation of unialgal cultures, measurement of dry weight, heterotrophic growth, measurement of nitrogen fixation, tolerance of blue green algae to pesticides,etc.