The Zhikong scallop spats’ (1.177～2.017 mm in shell length) diurnal rhythm of filtration rate were determined using static water method. For spats, the microalgae density was 3.0×104cell/ml and the temperature was 24±0.5℃, and for veliger, the microalgae density was 1.0×104cell/ml and temperature was 18±0.5 ℃. We measured the filtration rate of the veliger and spat at 17∶00，21∶00，01∶00，05∶00，09∶00，and 13∶00. Analysis showed that the filtration rate of the veliger and spat had similar diurnal rhythm. They had the lowest filtration rate(veliger: 0.002 6 ml/h•ind ,spat: 0.123 1 ml/h•ind) in the daytime(9∶00~13∶00) and the highest one(veliger: 0.025 8 ml/h•ind;spat: 0.509 6 ml/h•ind) in the night(21∶00~1∶00). There were significant difference between the highest and the lowest value（P<0.01）.