This research is a part of the research project of BOBLME (Bay of Bengal Large Marine Ecosystem) programme. The BOBLME covers 3.8 million sq km of sea area. The countries involved are Bangladesh, India, Indonesia, Malaysia, Maldives, Myanmar, Sri Lanka and Thailand. In this work, sea water samples were collected from Gadonkani area of Myanmar Deltaic Coastal Zone seasonally. Sampling sites were recorded with GIS positions. Some physicochemical properties (pH, DO, salinity, turbidity, total hardness, total alkalinity, TDS, TSS, TS, free carbon dioxide, BOD, COD, orthophosphate, organic phosphate, total phosphate, nitrite nitrogen, nitrate nitrogen and ammonia nitrogen) were determined. Trace metals (Cd, Pb, Hg, As, Fe, Cu, Zn and Mn) concentrations of the sea water samples were measured by atomic absorption spectrophotometer (AAS). Total petroleum hydrocarbons (TPHs) concentrations of sea water samples were measured as chrysene equivalence by using UVF spectrofluorometer. Oil and grease concentrations in sea water samples were determined by gravimetric-based method. Chlorophyll a contents of sea water samples were measured by UV-Visible spectrophotometer. Biological properties of sea water samples were investigated by membrane filtration method. All pH values of sea water samples ranging from 7.2 to 7.8 in the studied area are slightly basic. Maximum content of salinity (32 ppt) was recorded in the summer sample for sampling station (S5). The values of arsenic with range 1.19-1.75 ppb in summer samples were found under the permissible levels of ASEAN standard of 3.6 ppb but the contents of rainy and winter samples ranging from 5.30 to 9.44 ppb were above the acceptable levels of 3.6 ppb. All measured values of Cd with range 1.20-6.06 ppb were below the permissible levels of ASEAN standard of 10 ppb. All Pb contents with range of 4.02-8.11 ppb were below the permissible levels of ASEAN standard of 8.5 ppb. All measured values of mercury with range of 1.10-2.26 ppb were above the permissible levels of 0.16 ppb. The values of orthophosphate, organic phosphate and total phosphate were found to be (0.0160.352 ppm), (2.75-4.77 ppm) and (2.97-4.83 ppm) in seasonally collected samples. The values of DO, BOD and COD were recorded in the range of (4.80-6.20 ppm), (1.4-2.0 ppm) and (1.10-4.78 ppm). The measured DO values were within the permissible level of ASEAN standard (> 5 ppm) except the value of stations S4 for summer sample. Chlorophyll a distribution with the range of 1.207-1.981 mg/m3 was found in all of the study areas. Total petroleum hydrocarbons (TPHs) distribution over the sea water in the area of study was recorded as a range from 0.202 to 0.341ppm. The concentration distribution (50.00-100.16 ppm) of oil and grease over the sea water was recorded in all of study areas. All numbers of coliform counts were found under permissible levels of EPA standard (<1/mL) for all sea water samples. E.coli in all sea water samples was not isolated for seasonal sampling.