The purpose of this study was to evaluate the basic unit of irrigation water on golf courses in Jeju Island. The amounts of rainwater and groundwater used on 20 golf courses have been monitored for this study. The characteristics of rainwater and groundwater from the selected 20 golf courses were analyzed based on the existing data that had been collected for three consecutive years from 2006 to 2009. The range of monthly irrigation water (groundwater + rainwater) used was about 13,200～55,600 ㎥/month, with average of 36,600 ㎥/month. In the respects of the amount of annual water used, groundwater was recorded as 163,500 ㎥/year, and rainwater was recorded as 275,400 ㎥/year. Thus, the total annual irrigation water used was approximately 439,000 ㎥/year. The correlation (R2) between golf course lot size and average amount of monthly irrigation water used was 0.65, and the monthly basic unit per golf course area (1,000 ㎡) was calculated as 60 ㎥.