This study was undertaken to determine the normal serial ultrasonographic appearance of the postpartum uterine involution. Postpartum changes in uterine shape, architecture, echogenicity and diameter were monitored by ultrasonography in 10 Shih-tzu bitches. Serial ultrasonographic examination was done daily during the first week, 3 days interval from 8 to 30 days, and weekly from 31 to 100 days postpartum. All 10 postpartum bitches had normal involution by gross finding, vaginal discharges, and by ultrasonographic findings, uterine shape and echogenicity. The uterine diameter in the placental sites was decreased from $23.56{pm}1.45$ mm at 1 day to $14.08{pm}1.55$ mm at 7 day, and in the interplacental sites was decreased from $14.64{pm}1.28$mm at 1day to $9.61{pm}1.46$mm at 7 day postpartum. At 65 days postpartum the uterine diameter was 5-6 mm both placental and interplacental sites, and the uterine horns were uniform hypoechic, tubular structures without enlargement. Therefore, complete involution of the uterus occured 65 days. It was concluded that normal postpartum uterine involution in Shih-tzu bitches appeared to be completed 65 days postpartum by gross findings such as vaginal discharges, and ultrasonographic findings. And ultrasonographic characteristics of the postpartum uterine involution were described. Therefore, these result suggest that ultrasonographic assessment is a reliable method for diagnosing the subinvolution of placental sites and uterine dysfunction, such as pyometra in the bitch.