Abstract: Tetramethrin and S—5439 (Benzeneacetic acid, 4-chloro-α-( 1-methylethyl)— (3-phenoxyphenyl)methyl ester), two pesticidal components in "Julu", could be determined with gas chromatography using SF-30 as stationary liquid and n-C26—H54 as internal standard. The two pesticidal ccmponents were determined simultaneously with only one internal standard. In addition, some related conditions were investigated and the results were satisfactory. The recoveries were 102.7% (CV-1.3%) for tetramethrin and 99.6% (CV-2.3%) for S-5439. This method can be used in routine analysis and quality control.