Abstract: Net primary productivity of the Padma river, studied during February to December 2002, ranged between 0.13 and 0.54 mg O2 L-1 h-1 and community respiration rate was 0.15 to 1.04 mg O2L-1 h-1. In some occasions, community respiration exceeds the net primary productivity. Phytoplankton community was represented by 29 genera belonging to 6 families. Greatest crops of phytoplankton occurred in February where 26 genera of 5 families were recorded among which Chlorophyceae was abundant (38.46%) in terms of number of genera. Melosira sp., Synedra sp. and Fragilaria sp. (897.9x103, 129.1x103 and 117.1x103 ind. L-1, respectively) of Bacillariophyceae and Actinastrum sp., Schroederia sp. (378.7x103 and 204.1x103 ind. L-1, respectively) of Chlorophyceae were the most abundant genera. In June only 2 genera of 2 families were recorded. Although the common river alga, Melosira sp. was found most common in February and April, it was totally absent in June. Two pollution indicator algae viz., Arthrospira sp. and Oscillatoria sp. were found during the sampling period. Four different most commonly used diversity indices were calculated which were interrelated. The values of Shannon and Wiener Index of Diversity were 0.81 (minimum) in June and 5.1 in February (maximum). Species diversity (Shannon and Wiener index) increased with higher net production.