Protogyny is uncommon in caddisflies (Trichoptera) but does occur. I found protogyny in Lepidostoma satoi (Kobayashi, 1968) and L. complicatum (Kobayashi, 1968), while the congeneric L. itoae (Kumanski & Weaver, 1992) had a simultaneous emergence pattern of males and females. Dissection of the female internal reproductive organs revealed that the former two species had rather immature eggs, while the latter species had nearly mature eggs in the ovaries at emergence. Immature eggs needed 3 to 5 days to mature, but nearly mature eggs needed only 0 to 2 days. The mean longevity of females was 11.6 days in L. satoi, 10.4 days in L. complicatum, and 13.7 days in L. itoae. Male longevity in the former two species (4.6 days and 6.6 days, respectively) was less than the latter species (15.8 days). These results suggest that protogyny in L. satoi and L. complicatum is advantageous, allowing males to mate with mature females in a more timely manner, as the males can mate from the day of emergence. Protogyny at emergence may synchronize the mating period of the both sexes.