The current study was based on literature regarding socialized gender role norms and its application to a courtroom context. This project investigated the influence of expert witness smiling behaviors in men and women on ratings of perceived credibility by mock jurors. Potential interactions with participant endorsement of gender role norm stereotypes were examined. The current study also explored other variables that provided supplemental findings to hypothesized results. College students served as mock jurors for this project. Results supported previous research in which male expert witnesses were perceived by mock jurors as more likeable than female experts. Additionally, the current study replicated previous findings in which expert witness smiling behaviors led to increased ratings of likeability. However, smiling behaviors were not linked to attractiveness ratings of the expert witnesses. The results did not support hypothesized expectations in which endorsement of gender role norm stereotypes would interact with expert sex or smiling behaviors on ratings of credibility. However, participant endorsement of such stereotypes did contribute significantly to differences in ratings of the WCS subscales and total. Overall, participants with high endorsement of gender role norm stereotypes tended to rate the expert witness as lower in likeability, trustworthiness, knowledge, confidence, and credibility. The findings provide some evidence regarding the influences of expert witness sex and smiling, as well as juror stereotype biases, which may potentially affect expert witness credibility and testimony efficacy.