In this exploratory study, we analyzed the contribution of fathering to relational aggression (RA) in middle childhood and the moderating role of children's temperament and gender. Participants (N = 234; 46% girls) were attending public elementary school (mean age = 8.15; SD = 1.23) in middle-class neighborhoods in two Spanish cities. Fathers provided information about their parenting practices using the Parenting Styles and Dimensions Questionnaire, parents gave data on their child's temperament using the Temperament in Middle Childhood Questionnaire and children provided information about their peers' aggressive behavior using the Mini Direct Indirect Aggression Inventory. Fathering dimensions considered were Authoritative Cold, Authoritative Warm, Physical Punishment, and Insecurity; temperament dimensions considered were negative affect (NA), effortful control (EC), activity (AC), and shyness (SH). Gender, fathering, and temperament dimensions additively accounted for a significant proportion of the variance observed in RA. Several significant interactions suggested that the effect of fathering on RA was moderated by temperament and, in some cases, by children's gender. NA increased the potential risk of Authoritative Cold fathering (CF) and, in boys only, of Insecure fathering, while EC potentiated the protective effect of Authoritative-Warm fathering and, in boys only, buffered the risk effect of CF. SH buffered the risk effect of CF and decreased the protective effect of Authoritative Warm fathering on RA. Lastly, AC also buffered the risk effect of CF on RA. Results are discussed in light of the protective or the vulnerability role of temperament and in relation to models that explain sensitivity differences to environmental contexts.