Diel vertical migration (DVM) and horizontal distribution of Chaoborus flavicans larvae were studied in Lake Fukami-ike (maximum depth 7.75 m, Central Japan). The larvae showed a clear migration in the 4 ${sim}$ 7 m layer during the day and throughout the water column at night. It should be noted that, while old instar distributed throughout the column during the night. Young instar was found only in the 1 ${sim}$ 4 m layer. An examination of horizontal distribution revealed that larval stage was clearly related with the depth. It suggests that Chaoborus appear to exist in the deeper area during the larval stage.