Abstract: Ion chromatography was applied to the determination of ammonia in gas phase of mainstream smoke of cigarettes. IonPac CS16 cation analytical column and IonPac CG16 cotion guard column were used in IC, with 0.045 mol·L-1 of methylsulphonic acid solution as eluent. Conductivity detection was adopted. The linearity range of ammonia was 0.01-1.0 mg·L-1, with detection limit (3s) of 8.79×10-3μg·cig-1, and the lower limit of determination (10s) of 2.93×10-2μg·cig-1. Recovery rates obtained by standard addition method were in the range of 92.2%-103%. Both intra-day RSD and extra-day RSD (n=5) were less than 5.5%. The proposed method was used for determination of ammonia released from the mainstream smoke of 7 kinds of cigarettes.