The study was conducted to evaluate the effects of pH on the filtration rate of freshwater pearlmussel Lamellidens marginalis under laboratory conditions. Three treatments were used in triplicate;treatment 1 (T1) at pH 7.5, treatment 2 (T2) at pH 8.0 and treatment 3 (T3) at pH 8.5. Ten mussels werestocked in each aquarium with continuous aeration. After 48 hours, 40 ml eutrophicated water having 34.75 x105 to 36.0 x 105 cells/ml of phytoplankton were provided in each aquarium. Initial concentration ofphytoplankton was 14400±360.55, 13900±360.55 and 14133± 404.14 cells/ml, whereas the finalconcentrations were 10300±100.00, 8300±200.00 and 10333±57.73 cells/ml in T1, T2 and T3, respectively.The reduction rate was consistently lower in T2 when compared to other treatments. Mussels of T2 (pH 8.0)exhibited significantly higher filtration rate (p<0.05) over T1 (pH 7.5) and T3 (pH 8.5) at all sampling times.The minimum filtration rate 58.03±32.79 ml/mussel/h was found in T3 after 1 h exposure, whereas thehighest filtration rate 110.94 ± 21.68 ml/mussel/h was obtained in T2 after 2 h exposure. The resultsconcluded that the pH has a clear effect on feeding habit of freshwater pearl mussel and pH 8 providesenvironment friendly to maximize the filtration of L. marginalis.