Knowledge on the optimum environmental conditions for a potential aquaculture species is necessary to simulate such situation in an artificial setting. Geloina expansa is an economically- and ecologically-important bivalve which thrives in brackishwater mangroves or Nypa zones. Fluctuating salinity conditions may possibly affect the filtering capacity of G. expansa. Laboratory experiment was conducted to determine the effect of salinity concentrations and body size on the filtration rate and pseudofaeces production of G. expansa. The results indicated that filtration rates of the clams significantly increased (P < 0.05) at low salinities (7- 15ppt). Moreover, salinity levels did not affect pseudofaeces production. Additionally, filtration and pseudofaeces production were not affected by body size. These findings are vital for the development of aquaculture techniques for G. expansa in the Philippines.