Yellow pond turtle (Mauremys mutica) eggs were incubated in vermiculite under nine combinations of temperature and humidity, i. e., 25 degrees C and -12 kPa, 29 degrees C and -12 kPa, 33 degrees C and -12 kPa, 25 degrees C and -150 kPa, 29 degrees C and -150 kPa, 33 degrees C and -150 kPa, 25 degrees C and -300 kPa, 29 degrees C and -300 kPa, and 33 degrees C and -300 kPa, aimed to study the effects of incubation temperature and its interaction with substrate humidity on the embryonic development of M. mutica. The initial egg mass, incubation temperature, substrate humidity, and the interaction of incubation temperature and substrate humidity had significant effects on the mass increment of egg in the course of hatching. At the same temperature, eggs incubated in wetter substrates (-12 kPa) gained more mass than those incubated in drier substrates (-150 kPa and -300 kPa). Incubation temperature affected hatching period significantly, while substrate humidity and its interaction with temperature did not. Both incubation temperature and substrate humidity affected hatching success and shell crack rate significantly. Abnormal hatchlings were found when incubated at 25 degrees C and 33 degrees C, but not at 29 degrees C. Incubation temperature had significant effects on the hatchling mass, carapace length and width, plastron length and width, body height, and tail length; while substrate humidity only affected hatchlings plastron length. The interaction of incubation temperature and substrate humidity did not affect the morphology of hatchlings.