Abstract: To investigate the effects of fasting for 1—2 weeks on swimming performance, thermal tolerance and spontaneous activity juvenile Chinese sucker (Myxocyprinus asiaticus), the body mass and body length of 108 fish with (3.26±0.64) g and (5.32±0.32) cm were randomly divided into 3 groups, i.e., control group, 1 week and 2 weeks fasting group. Then, relevant parameters of swimming ability, thermal tolerance and spontaneous activity of these fishes were measured after different fasting times. Fasting for 1—2 weeks has no effects on the rest metabolic rate and critical swimming speed of M. asiaticus. Maximum metabolic rate, metabolic scope, cost of transport, head height/head length and body height/body length significantly increased in 1 week and 2 weeks fasting groups compared to that in control group (P<0.05). Fasting for 1—2 weeks has no effects on the critical thermal minimum and lethal thermal minimum of M. asiaticus. Critical and lethal thermal maximum significantly increased in 1 week and 2 weeks fasting groups compared to that in control group (P<0.05). Fasting for 1—2 weeks has no effects on the total movement distance, average movement speed and percent time spent moving of M. asiaticus. Our results suggested that aerobic swimming capacity and spontaneous activity of M. asiaticus was not affected by fasting for 1—2 weeks, which may be beneficial for maintaining their daily foraging activities. Moreover, fasting for 1—2 weeks has no significant impact on the low-temperature tolerance, but this stress can improve the high-temperature tolerance of M. asiaticus.