The present study was designed to delineate the duration of postpartum estrus in the prairie vole, Microtus ochrogaster. Breeding pairs were separated prior to parturition, and males were reintroduced to the females 0–12 h, 12–24 h, 24–48 h, or 48–72 h postpartum. Pairs were observed for 1 h to determine whether mating occurred. Eighty percent of females in the first two time intervals were receptive within 24 h of parturition, 60% of females in the third time interval mated with males 24–48 h postpartum, and only 10% of females in the final time interval mated 48–72 h following parturition. These results indicate that postpartum estrus in this species typically lasts only 24–48 h.