We conducted population surveys of freshwater turtles in Diaoluoshan National Nature Reserve, Hainan Province, China, from 2012 to 2019, capturing 20 individuals belonging to 4 species, including 2 native species (big-headed turtle [Platysternon megacephalum] and Hainan four-eyed turtle [Sacalia insulensis]) and 2 alien species (red-eared slider [Trachemys scriptia elegans] and common snapping turtle [Chelydra serpentia]). We captured 12 big-headed turtles and estimated their population density (1.6514 individuals/km) and abundance (14 individuals), both of which indicate that Diaoluoshan National Nature Reserve is an important area for turtle conservation, especially for big-headed turtles.