Objective:To explore whether there is mood congruency effect of involuntary autobiographical memories among different mood undergraduates.Methods:Totally 60 college students were induced to generate positive,negative or neutral mood by emotional pictures and music.Vigilance task paradigm was used to induce involuntary autobiographical memory in the present experiment.All participants were asked to rate the pleasantness of involuntary autobiographical memories,then the memory proportion of different valence was calculated.Two raters who had not taken part in the experiment were instructed to divide the objective memory contents into positive,negative and neutral three types.Furthermore,the number of involuntary autobiographical memories recalled was evaluated according to the valence of objective memory contents.Besides,all participants were asked to rate the mood state at the end of the experiment.Results:There was no significant difference in pleasantness ratings among different mood college students (P ＞ 0.05).There was a significant interaction between mood state and the valence of objective memory contents (P ＜ 0.01).Further examination of the interaction suggested the number of positive memory contents recalled was greater in positive state compared with neutral state [(6.3 ±5.5) vs.(2.8 ±2.2),P ＜0.01].However,there was no difference in the number of negative memory contents and neutral memory contents among different mood states (Ps ＞ 0.05).Additionally,no matter the pleasantness ratings was positive or negative,there was no significant correlation between the proportion of memories and mood state rated at the end of the experiment (r =0.29,-0.13,Ps ＞ 0.05).Conclusion:It suggests that there does not exist mood congruency effect of involuntary autobiographical memories among college students in different mood states.Even in negative mood state,their involuntary autobiographical memories would still display a kind of optimistic bias.