Abstract: Two methods,gas chromatography( GC) and gas chromatography- mass spectrometry( GC- MS) were proposed for the determination of n- Docosane and n- Octacosane,which were the index components of paraffin illegally added into sweet potato vermicelli.After wet digestion,extracted with petroleum ether( b.p 30~60 ℃),the samples were drying with rotary evaporation.Subsequently,the analytes were analyzed by GC and GC- MS after dissolved with n- hexane.The recoveries of n- Docosane and n- Octacosane in GC method were 80.7% ~82.5% and 83.4% ~86.2%,respectively,with the relative standard deviations 8.2%~9.9% and 7.8% ~9.3%,while those of GC- MS method were 81.1% ~84.5% and 80.0% ~86.7%,and the relative standard deviations were 7.2% ~9.8% and 6.5% ~9.2%,respectively. The limit of detection( LOD) and the limit of quantitation( LOQ)about n- Docosane were 2.4 mg / kg and 3.8 mg / kg separately in GC,while those of n- Octacosane were 1.8 mg / kg and3.3 mg / kg. In GC- MS,the LOD and LOQ of n- Docosane were 0.1 mg / kg and 0.2 mg / kg,while those of n- Octacosane were0.05 mg / kg and 0.07 mg / kg separately.Compared with GC,GC- MS had a better performance about specificity,sensitivity and quantification,and this method was suitable for the detection of paraffin added illegally in sweet potato vermicelli.