Oxycodone is known to be effective in pain control and has less sedative effect than morphine does. It has been described that distribution of cytochrome P450, which is associated with metabolism of oxycodone, differed between the races. Proper dose of intravenous oxycodone after major abdominal surgery has not been well defined in Korean. The purpose of this study is to evaluate the optimal dose of intravenous oxycodone for pain control after laparoscopic colorectal surgery in Korean based on pain score and side effects.