The study reported here was conducted to evaluated the effectiveness of leaf temperature in estimating crop water stress. Firstly, a SPAC model was developed to examine the relationship between leaf temperature and soil moisture. Secondarily, experimental tests were persued on the relationship between soil moisture condition and crop indices such as leaf water potential, leaf temperature, leaf-air temperature difference. It was observed that leaf-air temperature difference showed drastic response to the irrigation treatment. Infrared leaf temperature measurement were made at Miyako island, Okinawa where suffered severe drought from July to August in 1983. The investigated data showed that sugarcane leaf temperatures with lack of soil water were almost always heigher than the temperatures with no shortage of soil water. These results obtained above will effectively be used for the irrigation scheduling.