Vasopressin and its’ interactions with the vasopressin 1a receptor (V1aR) are important in the formation of social attachments and parental behavior in male mammals but there also is evidence that vasopressin is involved in maternal behavior in female mammals. Laboratory studies have shown that female rats with greater expression of V1aR in particular brain regions display more maternal behavior than those with less V1aR expression. Previous data showed that variation in neural V1aR expression in males of several species of rodents was influenced by the length of microsatellite DNA within the regulatory region of gene (avpr1a) encoding V1aR. In male prairie voles (Microtus ochrogaster), the neural expression of V1aR differs between individuals with longer versus shorter avpr1a microsatellites. Males with longer avpr1a microsatellites had greater V1aR expression in particular brain regions, spent more time with their female social partner, and licked and groomed pups more than males with shorter avpr1a microsatellite lengths. If avpr1a microsatellite length is correlated with V1aR expression in females in a similar fashion to that in male prairie voles, females with longer avpr1a microsatellites should have greater reproductive success since maternal care should be critical for offspring survival. In addition, female prairie voles may benefit by living with males that have longer avpr1a microsatellites due to increased male presence at the nest and paternal care. We tested these predictions with prairie voles from semi-natural populations. Females that had summed avpr1a microsatellite allele lengths greater than the median produced more litters and total offspring than females with summed avpr1a lengths less than the median. Females with summed avpr1a microsatellite allele lengths greater than the median also produced offspring sired by more males. The avpr1a length of male social and genetic partners did not influence female reproductive success. This is the first field study showing a relationship between avpr1a microsatellite allele length and female reproductive success in any species.