Abstract: Swimming and breathing behaviours of a captive baiji Lipotes vexillifer were observed in a Baiji Aquarium from May to October 1992.Swimming speeds could be divided into 3 types:slow swimming (SS),middle-speed swimming (MS) and fast swimming (FS).SS was the most common swimming pattern.The average time portion of SS per hour in daytime and at night showed no significant difference,however MSs and FSs portions were obviously greater in daytime than those at night.It can be seen that baijis movement slowed down at night was due to the lower occurred rates of MS and FS,but not increasing SS time portion.The average breathing per hour was 106.05 times (1.77 times per minute).The mean of breathing interval was 30.62±24.55 s,ranging between 1.04-316 s.The respiration model of the baiji was cycles of one long interval breathing accompanying with 1-8 short interval breathings.SSs time portion per hour showed no obvious influence on breathing frequency of the baiji,but the frequency showed significant positive correlation with MSs and FSs time portions per hour.It was deduced that MS and FS would significantly increase the energy consumption by getting more air in comparison with SS.