Abstract: A derivative GC method with n-tetracosane as the internal standard was developed for the determination of L-sorbose prepared by bioconversion and residual D-sorbitol in it. The method includes two procedures. The first procedure involves acetylation of bioconversion samples with a solution of acetic anhydride: pyridine(1∶1) at 90℃ for 20 min. The resulting products were assayed by GC to determine residual D-sorbitol. The second procedure involves reduction of the bioconversion samples with NaBH₄ in aqueous solution at 40℃ for 1 hour followed by reaction with the mixture of acetic anhydride: pyridine(1∶1) at 90℃ for 20 min. The resulting products were assayed by GC to determine L-sorbose. Chromatography was performed on a 5% OV-17 stainless steel column(2 m×3 mm ID) with nitrogen as carrier gas. The detector was FID. The standard curves of D-sorbitol and L-sorbose were linear in the ranges of 0.01999～2.999 μg and 4.000～24.000 μg respectively. The method has been applied to assay L-sorbose and residual D-sorbitol in bioconversion products and to monitor bioconversion termination point of L-sorbose.