Using an ambulatory data-logging system, 1) rectal temperature, 2) vaginal temperature, 3) skin temperature, 4) air temperature at 5cm above the chest band (5cm temperature), 5) heart rate, 6) respiratory rate, 7) number of jaw movements and 8) number of pauses between jaw movements longer than 3sec were recorded simultaneously for grazing adult Holstein cow in a hot summer environment.The apparatus was mounted on the back of the cow. Grazing and rumination periods were distinguished from jaw movements or jaw movements and pauses vaginal temperature. Twenty four-hour relationships among rectal, vaginal, skin and 5cm temperature, heart rate, respiratory rate and grazing and rumination behavior in a hot environment were considered. It was estimated from the 5cm temperature whether the animal sheltered in the shade during the day or returned into the sun. The present ambulatory data-logging system is a useful tool for analyzing the physiological and behavioral variables of free-ranging cattle for over 24 hours in a hot environment.