Objective:To explore the effect of emotional faces on startle reflex in adulthood.Methods:Thirty-six normal adults were recruited through advertisements and screened out with State-Trait Anxiety Inventory and Beck Depression Inventory.Subjects were presented with acoustic startle probes,while viewing different facial stimulus(representing anger,fear,sad,happy,and neutral).Their orbicularis electromyography(EMG)activity and self-reported valence and arousal ratings were assessed.Results:Anger and fear expressions both induced greater startle reactivity than neutral expressions[(52.07±4.24),(50.92±4.87)vs.(47.41±4.49),Ps0.05],but the differences between other faces were not significant(Ps0.05).Self-reported valence and arousal ratings both revealed significant main effects(F1=92.933,P0.001;F2=16.800,P0.001).Valence ratings for happy expressions(6.52±1.11)were rated significantly more positively than other types of expressions(anger 3.42±0.86,fear 3.58±1.02,sad 3.61±1.00,neutral 4.55±0.82).Neutral faces associated with significantly higher valence ratings than anger,fear and sad faces,which were not significantly different from each other(Ps0.05).For self-reported arousal,anger(5.03±1.74)and fear faces(5.05±1.55)were significantly higher than the other types(sad 4.57±1.34,happy 4.23±1.43,neutral 3.64±1.41),whereas arousal ratings for neutral faces were significantly lower than the other types,and there were no other significant differences(Ps0.05).Conclusion:The findings suggest that there is not a one-to-one relationship between expression valence and startle reflex.Startle reflex modulation effect seems to be found only for anger and fear faces.