This experiment was conducted to evaluate the effect of different diets on the growth, body composition, glycogen, survival rate of hard clam as well as bacterial flora and water quality in hard clam pond. Four experimental diets were algae, eel meal, organic fermentative solution mixed with eel meal, and organic fermentative solution. After six month of culture, the result showed that eel meal and algae groups had significantly better growth and survival rate than other groups. The organic fermentative solution mixed with eel meal group had significantly lower glycogen than other groups. The algae group had significantly higher body crude protein than other groups. No significant differences were found in body crude lipid, moisture, and condition factor among the four groups. The survival rate in algae and eel meal groups were 94.31% and 91.46%, respectively, and these were better than the others. The lowest value was found in group fed with organic fermentative solution mixed with eel meal (12.3%). During the experimental period, the total bacterial number was 1.01´103-2.83´104 CFU/ml and no increase was observed with time. The bacterial flora varied with culture period. The species diversity index of bacteria was high in the initial stage of this experiment. The Vibrio spp. and Aermonas spp. predominated in the final stage, because these ponds had less death and lower survival rate. During the experimental period, the organic fermentative solution group had the worst water quality.