Recent reports suggest the relationship between the decrease in the body temperature and hypotension or the onset of diabetes mellitus, in people whose normal temperature is more than 36.5 degrees. Autonomic nervous system regulates blood flow, thermogenesis, and glucose and adipose metabolisms, therefore, it is important to keep the autonomic function adequately for preventing the circulatory and metabolic diseases. The contrast bath therapy is one of rehabilitation therapies. In usual way, the body part is immersed in warm bath for 4 minutes, then in cold bath for 1 minute, and this procedure is repeated 5 times. This therapy improves local blood circulation through vasodilatation and vasoconstriction. Furthermore, immersion of the body part in cold water activates the parasympathetic function. In this study, we examined whether or not longer immersion time in cold water improves parasympathetic function and prevents the skin temperature from decreasing. Twenty healthy subjects (10 men and 10 women: mean age 22.0±1.8 years old) with no history of any pathological condition were recruited. All subjects signed an informed consent before participating in this study. A hand was immersed for 4 minutes in cold water and for 1 minute in warm water, and this procedure was repeated 5 times in this contrast bath. The contrast bath was performed twice or three times a week and was continued for four weeks. We carried out cold immersion test in which a hand was immersed in 10 degrees of water for 16minutes before starting and after completing a series of the contrast bath. RR interval were monitored by electrocardiograph during cold water immersion test, and a high-frequency (0.30 – 0.40 Hz) RR interval variation was analyzed by FFT to quantify parasympathetic activity. After cold water immersion test, the skin temperature was immediately measured on the proximal nail fold of the index finger. Paired t-test and Scheffe’s test were used to analyze the change of skin temperature and electrocardiogram, respectively. The skin temperature did not decrease by cold water immersion test after 4 weeks of the contrast bath whereas it significantly decreased before starting the contrast bath. Moreover, parasympathetic activity significantly increased 10 minutes after cold water immersion in the test by performing 4 weeks of the contrast bath. Present results suggest that longer cold water immersion time in the contrast bath stimulates parasympathetic nervous system, increases blood circulation in the periphery, and keeps skin temperature of the finger-tip.