The correlation between arousal state and fetal habituation was tested. Four behavioral states were determined according to fetal heart activity and movement pattern in 52 fetuses. Repeated wide low-frequency sound was used as external stimulus. Ceasing of response to 5 consecutive stimuli indicated habituation. The time from response to habituation was defined as habituation time. Although fetuses in a lower arousal state habituate more rapidly, the difference is not statistically significant.