This paper deals with the determination of free nicotine in tobacco leaves by modified chloroform extraction and UV spectrophotometer, and the optimum extraction time and dose of chloroform. The results indicated that the free nicotine in 1g tobacco sample could be entirely extracted by 50 mL CHCl3 in 30 min. By use of UV spectrophotometry, the recovery of free nicotine in tobacco leaves reached 88.4% with high repeatability.