L-menthylformaldehyde was synthesized by the reaction of the Grignard reagent derived from menthyl chloride with N,N-dimethylformamide (DMF) in tetrahydrofuran by one-step process. The influence of the material ratio, reaction temperature and reaction time on the yield of the product had been investigated. The optimal reaction condition was the Grignard reagent reaction with 1.2 equivalent of DMF at 20oC for 4 hours. Under optimal reaction condition, the yield was 42.6% and no stereoisomer yielded.