To examine the biological effects of tributyltin (TBT) exposure, the caprellid amphipod, Caprella danilevskii, was exposed to five levels (0, 10, 100, 1000 and 10 000 ng l−1) of TBT during the embryonic stage (five days). Although the female proportion was 36% of the total in the control, the female proportion changed dramatically in the hatched juvenile, i.e. the proportion of females was found to increase to 55·6% at 10 ng l−1, 85·7% at 100 ng l−1, and 81·8% at 1000 ng l−1. All specimens died in 10 000 ng TBTCl l−1 within five days after spawning due to the acute toxic concentration for the species. Reproductive inhibitions such as brood loss and oogenesis inhibition occurred even at 10–100 ng TBTCl l−1 exposures in the short-term period in both parental females and their offspring females. The embryo survival rate in the offspring decreased drastically as the TBT concentrations increased, with the decrease being observed at TBT concentrations as low as 10 ng l−1 (69%) during the five days. In parental females, the survival rate also decreased at more than 100 ng TBTCl l−1, despite movement after five days into seawater with no TBT added. Data suggest that nanogram concentrations of TBT similar to those encountered in coastal waters around the developed countries can directly affect sex proportion, reproduction, and survival in the caprellid.