Previous research using self-report measures found that the Big-Five personality trait openness to experience was the strongest predictor of attitudes toward gay men and lesbians. A secondary data analysis was conducted to evaluate the mediation between openness levels and the time to intervene as a bystander to an anti-gay aggressive scenario. Participants (n = 65) were self-identified heterosexual male undergraduate students who witnessed a staged scene of anti-gay aggression. During the experiment, one confederate was verbally aggressive toward another, ostensibly gay, confederate; participants chose whether and when to intervene. Participants then completed a battery of measures, including the Big Five Personality Inventory (BFI), and the Attitudes Toward Lesbian and Gay Men Scale (ATLG). Openness to experience significantly predicted attitudes toward gay men, which in turn significantly predicted participants’ the time it took participants to intervene. The results highlight the importance of examining both attitudes and personality traits in predicting bystander behavior. These findings may inform bystander intervention techniques and other programs aimed to reduce anti-gay aggression.