ObjectiveTo explore the correlation between visual P300 changes of patients with social phobia induced by facial expression stimuli and the therapeutic effect.MethodsA total of 40 patients with social phobia were assessed by a self-designed demographic questionnaire and Liebowitz Social Anxiety Scale (LSAS). The examination of visual P300 induced by three facial expression stimuli, i.e. happy, peace, and disgust, was conducted before treatment and 6 months after treatment.ResultsThe P300 amplitudes (7.20±2.95) μV induced by disgust after treatment were lower than those (9.55±4.35) μV before treatment(P<0.05). The changes of LSAS scores positively correlated with the changes of P300 amplitudes induced by disgust (P<0.01).ConclusionThe decrease of P300 amplitude may be a state sign of social phobia.