Abstract: Ten behavioural patterns——clockwise swimming, counterclockwise swimming, swimming on back and side, rolling, upright positioning, playing, sexual behaviour, fish catching and resting——were observed during April 1985-March 1986 from a male Lipotes in captivity for over six years. The statistics of variation in the behavioural patterns indicated that there were obviouscircadian rhythms and seasonal rhythms. The clockwise swimming often occurred at night, and the counterclockwise swimming usually took place in the daytime. The total duration for either type of swimming in the course of 24 hours was nearly equal.The typical resting behaviour occurred at night, with peaks in January and May-August. There were obvious peaks of sexual behaviour during April-May and August-September. Rolling swimming occurred in the morning and after feeding during the day, and had three peaks, correlated to the condition of the dolphin pool. The circadian respiratory rhythm was not evident.