Purpose The purpose of this study was to understand how the family system plays a role in knowledge sharing (KS) within family firms. The authors argue that the family’s influence can occur through two routes. An external route in which the family affects the culture of the organization and through an internal route in which family leadership within the firm affects the practices and behaviors within the business. Design/methodology/approach Data for this project came from the survey responses of 93 Spanish family firms. Findings The findings expand previous understanding about KS in family firms by outlining the two routes through which the family can have positive effect on KS within family firms. Results show that family system characteristics (i.e. next-generation commitment, family trust and intergenerational relationships) affect KS through their impact on the participative culture of a family firm. Additionally, when a family has been in control of the business for more generations, they place higher importance on family legacy and continuity, which is likely to strengthen the relationship between participative culture and KS in family firms. Originality/value Given the important role that the family system plays within the family business, this paper explored how family characteristics can influence KS in family firms. The authors contribute to the literature by highlighting the importance that the owning family can have in creating an environment that can facilitate KS in family firms.