This study was conducted to determine effects of different pH on the flocculation ability of chitosan and utilization flocculated algae for feeding sweet snail larvae. In 1^st experiment, Chaetoceros algae were flocculated by chitosan at three pH levels: non-change, 7 and 5. At pH 5, flocculation reached the highest efficiency (91%) after 4 hours. In 2^nd experiment, flocculated algae were kept in temperature of 4^oC in 15 days to determine the viability. At non-change pH treatment (pH= 9.3) Chaetoceros obtained highest cell viability (52.23%). After re-inoculation at initial density of 500,000 cells/mL, the highest cell density was obtained at day 15 in pH 7 (8,750,000 cells/mL). In 3^rd experiment, flocculated algae were used for feeding sweet snail larvae in 20 days. Results showed that the shell length and height of larvae obtained highest values after 7 days with non-change pH (1094.40 and 852.77 µm, respectively). Highest survival rate was also recorded in this treatment (89.6 %). Our finding indicated the necessary to maintain pH values from 7,0-9,0 in order to gain the high algal cell viability after flocculation and effectiveness for feeding sweet snail larvae.