Abstract About 2.6 million third-trimester stillbirths occur annually worldwide, mostly in low- and middle-income countries. However, the causes of stillbirths are rarely investigated. We performed a retrospective, hospital-based study in Zhejiang Province, southern China, of the causes of third-trimester stillbirths. Causes of stillbirths were classified using the Relevant Condition at Death classification system. From January 1, 2013, to December 31, 2018, we enrolled 341 stillbirths (born to 338 women) from 111,275 perinatal fetuses (born to 107,142 women), as well as 293 control cases (born to 291 women). The total incidence of third-trimester stillbirths was 3.06/1000 (341/111,275). There were higher proportions of women with a high body mass index, twins, pregnancy-induced hypertension, assisted reproduction and other risk factors among the antepartum than the control cases. The antepartum stillbirth fetuses were of lower median birth weight and gestational age and had a smaller portion of translucent amniotic fluid than the control cases. The antepartum stillbirth fetuses had a higher frequency of abnormalities detected prenatally and of fetal growth restriction than the control cases. Of 341 cases (born to 338 mothers), the most common causes of stillbirth were fetal conditions 117 (34.3%) cases, umbilical cord 88 (25.8%), maternal conditions 34 (10.0%), placental conditions 31 (9.1%), and intrapartum 28 (8.2%). Only eight (2.3%), three (0.9%), and two (0.6%) stillbirths were attributed to amniotic fluid, trauma, and uterus, respectively. In 30 (8.8%) cases, the cause of death was unclassified. In conclusion, targeted investigation can ascertain the causes of most cases of third-trimester stillbirths.