The effects of MS-222, an anaesthetic for fish, on behaviors of Danio rerio were examined under laboratory condition.The results showed that the behavior of anaesthotized D.rerio was a gradual process, and four narcotic stages of fish behavior, non-anarcosis(Ⅰ), light anarcosis(Ⅱ), mediate anarcosis(Ⅲ), and deep anarcosis(Ⅳ), were defined in the present study.The time of the fish being in a certain narcotic stage was not familiar under different concentrations of MS-222.When exposing to high dosage of anaesthetic for 15min, fish in the water with MS-222 concentration of 80-90 mg·L^-1 was in Ⅲ narcotic stage and all fish survived, but more than 90%of fish above 100 mg·L^-1 of MS-222 finally died.In the experiment of conditional reflex of feeding, four treatments, photic stimulation but not anesthesia (P), neither photic stimulation nor anesthesia (NN), photic stimulation and anesthesia (PA), and not photic stimulation but anesthesia (A), were set.The time from putting the feed into the water to fish eating the feed in treatment P, NN, PA, and A was 12.06±1.34s, 13.20±1.13s, 56.56±56.48s and 36.20±25.74s, respectively.It was shown that MS-222 prolonged the time of conditional reflex.The present research could give an advice in using MS-222 in experiments and fish transportation.