Objective To investigate the effect of circadian propofol anesthesia on spatial learning and memory in rats using the morris water maze (MWM).Methods Male SD rats were randomly divided into three groups (n=8 in each group):group control(group C:10％ fat emulsion was administered 0.5 mg·kg1·min-1 from 08:00 to 12:00 and from 23:00 to 03:00),group light (group L:pmpofol was administel 0.5 mg·kg-1 ·min-1 from 08:00 to 12:00 and 10％ fat emulsion was administered 0.5 mg·kg-1 ·min-1 from 23:00 to 03:00) and group dark (group D:10％ fat emulsion was administered 0.5 mg·kg-1·min-1 from 08:00 to 12:00 and propofol was administered 0.5 nmg· kg-1· min-1 from 23:00 to 03:00).All the rats were housed under a light/dark cycle (light phase is 07:00-19:00).After propofol was stopped in group L and group D and fat emulsion was stopped in group C,the rats were subjected to MWM on 4 consecutive days.Both the latencies of finding a hidden platform in the water maze and the annulus-crossing index were recorded to evaluate the spatial learning and memory.Results There was no difference among three groups on the first day (P＞0.05).The escape training latency in group L and group D were longer than that in group C on the second day (P＜0.05).On the third and fourth day,the escape training latency in group L was significantly shorter than that in group D but was longer than that in group C (P＜0.05).Meanwhile,The annulus-crossing index in group L was better than that in group D but was less than that in group C(P＜0.05).Conclusions The influence of propofol anesthesia on spatial learning and memory was pronounced when administered during the dark phase than that when administered during the light phase.