•Men showed a testosterone increase after a dyadic competition and female exposure.•Self-reported and observer-rated personality state changes were detected.•Testosterone reactivity moderated some of these, partly attenuated by cortisol.•These findings provide interesting insights into hormone-personality response-links. Increases in men’s testosterone (T) levels after intrasexual competitions and exposure to females facilitate competitive and courtship behaviours, suggesting T reactivity should affect relevant personality state changes. How exactly T reactivity, also under potential buffering effects of cortisol (C), relates to personality state changes is unclear. In a preregistered study, we aimed at inducing T increases in young men (N = 165) through dyadic intrasexual competitions while exposed to a female experimenter. We investigated self-reported and video-based observer-rated personality state changes, captured by the interpersonal circumplex and social impressions, in relation to hormonal levels. Results revealed increases in self-reported competitiveness and observer-rated self-assurance, relative to a control group, moderated by T reactivity and partly by T × C interactions, providing insights into hormone-personality response-links.