<p>Behavioural studies have shown that social comparison between oneself and opponents influences certain prosocial behaviours such as helping and cooperation behaviours towards opponents. However, it is uncertain whether social comparison affects other prosocial behaviours. More importantly, no studies have directly investigated whether social comparison affects antisocial behaviours towards opponents or neural mechanisms underlying both prosocial and antisocial behaviours. The present study addresses these issues by investigating the effects of social comparison on spreading positive and negative information about an opponent and the corresponding neural activity. To this end, thirty participants in the present study completed a card-drawing task, and compared their outcome with those of an opponent, obtaining better, worse or equal outcomes. Subsequently, they viewed positive or negative information about the opponent and indicated the proportion of other opponents to whom they would spread this information. Behavioural results showed that, compared to participants in the better and equal conditions, those in the worse condition were less likely to spread positive information and more likely to spread negative information. Event-related potential results showed that the worse condition enhanced early frontal late positive potential (LPP) responses to positive information compared to the better and equal conditions, and middle and late LPP responses compared to the better condition. Furthermore, both the worse and better conditions increased late central LPP responses to negative information compared to the equal condition. The findings suggest that social comparison influences the spreads of positive and negative information about opponents and relevant neural responses.</p>