Abstract: Manganese content is an important index to evaluate the quality of gasoline. In this work, a new method of GC/MS was developed for determination of the manganese content in gasoline using direct injection and external standard. Methyl-cyclopentadienyl-manganese-tricarbonyl (MMT) additive composition was studied, which was used in Jiujiang subcompany production site of SINOPEC. The optimum conditions for analysis instrument were determined by orthogonal experiment. The quantitative curves of manganese in gasoline were established using ethanol as solvent. The method is simple, rapid, sensitive, accurate, and the minimum detection amount is 0.57 pg. The relative standard deviaton is less than 6% and the recovery of standard addition is from 90% to 110%. By comparison with the atomic absorption spectrometry method of Jiujiang subcompany quality control center, the determination results of the two methods have good consistency, the absolute value of the relative deviation is less than 8% in the oil sample analysis.