A large number of studies have identified several direct costs of sexual harassment, including energy expenditure and reduced foraging ability. However, the fitness consequences of sexual harassment over a longer time-scale have never been investigated. Here, we estimated the effects of male sexual harassment on female fitness in the guppy, Poecilia reticulata, a small tropical fish in which sexual conflict over mating rates is particularly pronounced. We compared the lifetime fecundity and survival of two groups of females exposed to different levels of sexual harassment. We further estimated the effect of sexual harassment on the fitness of the second generation by raising the offspring to maturity and measuring traits associated with fecundity in daughters and with pre- and post-copulatory competitiveness in sons. Although sexual harassment did not reduce mothers’ lifetime fecundity, it affected their timing of reproductive allocation. Interestingly, sexually harassed females produced daughters with smaller body size and sons that were less attractive to females and less successful in achieving coercive copulations than the sons of control females. This study provides compelling evidence that sexual harassment can have negative cross-generational fitness effects, suggesting that its consequences on female fitness may be more profound than currently thought.