This study was carried out in four selected stations (Mohonpur, Kaligonj, Charludua and Daulatkhan) in the Meghna river system, Bangladesh between the latitude 22°35.494Ñ N - 23°23.987 N and longitude 90°35.793 E - 90°49.061Ñ E. Average net primary production (NPP) and gross primary production (GPP) (gC·m3 ·h) in the euphotic zone of the Meghna river were 0.089 ± 0.021 and 0.161 ± 0.025 respectively. The rate of conversion of GPP into NPP ranged between 48.17 and 62.63% with an average of 54.72%. The mean ratio of NPP to GPP (NPP:GPP), NPP:Respiration and average percent respiration rate to GPP were 0.549 ± 0.060, 1.251 ± 0.320 and 45.04 ± 6.02% respectively. The mean photosynthetic production for the day (gC·m3 ·day) and year (gC·m3 ·yr) were 1.930 and 704.45 respectively. Annual computed fish yield in relation to gross carbon synthesis was 7.0 kg fish·m3 ·year. The actual production of fish from the Meghna river is accounted about 0.21% of the estimated production. The gross energy production (Kcal energy·m3 ·day) by the producers was estimated about 18.0. The NPP of phytoplankton established a high significant negative correlation (r = -0.975; p < 0.01) with water temperature and low, but a definite negative correlation existed (r = -0.767) between GPP and water temperature.