Abstract: Objective To explore the relationships between pessimistic attitude to human nature,affective empathy and prosocial behavior,and to test the mediator effect of affective empathy on the correlation between lack of faith in human nature and prosocial behavior.Methods The Kiddie Machiavellianism Scale,Basic Empathy Scale,and Strength and Difficulties Questionnaire were used to investigate 101 middle school students.Results The girls had higher scores in affective empathy than boys(30.93±4.98 vs 28.62±5.15,P<0.05);students of grade 8 had higher scores in lack of faith in human nature than students of grade 9(17.47±4.40 vs 14.97±3.66,P<0.05);students of grade 9 had higher scores in affective empathy and prosocial behavior than students of grade 7(30.97±4.02 vs 7.82±1.65,P<0.05;27.50±5.45 vs 6.75 ±1.74,P<0.05).Lack of faith in human nature,affective empathy,and prosocial behavior were significantly correlated with each other(P<0.05-0.01).Affective empathy had a mediator effect on the relationship between lack of faith in human nature and prosocial behavior,accounting for 35.33% of total effect.Conclusion Gender difference is significant in affective empathy.The levels of affective empathy and prosocial behavior increase with the age and the effect of lack of faith in human nature on prosocial behavior is mediated by affective empathy.