This study was undertaken to determine the normal appearance of the postpartum uterine involution. Postpartum changes in uterine shape, architecture, echogenicity and diameter were monitored with ultrasonography in 8 Miniature Schnauzer dogs. Vaginal discharge was observed visually during the 3 weeks of postpartum. A large amount of viscous dark green discharge changed progressively to a small amount of transparent discharge. In the uterine shape, the transverse images were crescent or polygonal at the beginning, but became circular after 16 days. At postpartum day 24, the longitudinal images of placental and interplacental sites were similar to each other The echogenicity of uterine structure was clearly distinguishable among the hyperechoic serous membrane, hypochoic myometrium, hyperechoic endometrium, and anechoic uterine contents during the first week postpartum, but afterward the interluminal boundaries and echogenicity became obscure gradually. In addition, the anechoic substance of the endometrial cavity was not observed after postpartum day 28. In the uterine diameter, the diameter of placental sites decreased markedly from 24 mm at the first day postpartum to 13 mm at day 7, and the diameter of interplacental sites decreased from 15 mm at postpartum day 1 to 10 mm at day 7. At postpartum day 65, the uterus (6.4 mm) changed little and had a uniform homogenous echo, and thus it was confirmed that uterine involution was completed at that time in Miniature Schnauzer dogs.