Objective    To investigate the influence of D-cycloserine (DCS) on the long-term retention of rat extinction memory of conditioned fear.     Methods    Forty healthy male adult SD rats were randomly divided into five groups (n=8): a blank control group

an extinction control group

an extinction training group

a group with DCS treatment before extinction training

and a group with DCS treatment after extinction training. Following fear conditioning

which includes auditory conditioned stimulus (CS) paired with foot-shock unconditioned stimulus (US)

rats received non-reinforced exposure to CS for extinction training. CS-elicited freezing test for fear assessment and open-field test were conducted 3 d after extinction training.     Results    The percentage of freezing time of the extinction training group[（39.77±22.69）%] was significantly lower than that of the extinction control group[（61.46±11.10）%] (P0.05)

but significantly higher than that of the blank control group[（2.82±1.27）%] (P0.01). The percentage of central distance and standing frequency of the extinction training group [(2.82±2.89)% and 7±4] in the open-field test were both significantly higher than those of the extinction control group [(0.50±0.84)% and 3±4]

but lower than those of the blank control group [(19.29±6.08)% and 20±6] (P0.05). The percentage of freezing time and open-field test score of the group with DCS treatment after extinction training were significantly different from those of other four groups (P0.05).     Conclusion    DCS administration after extinction training promotes long-term retention of extinction memory of conditioned fear.