Abstract: A method for indirect determination of Vit B12 in health-care food by GFAAS was studied and reported in this paper.The sample was digested with mixed solution of conc.HNO3 and H2O2 (10+3) with microwave digestor,and Co2+ was dissociated completely by addition of HCl (1+99).Vit B12 was determined indirectly by GFAAS determination of content of cobalt in the sample.The working conditions of the instrument,including detection wavelength,lamp current,rate of carrier gas were described in detail.Influential factors,including the concentration of acid ,kinds of matrix modifier,the working condition of graphite furnace,and interferences of coexisting ions were studied and optimized.Linear relationship between values of absorbance and Vit B12 concentration ranged in 0.31-4.6 mg·kg-1 was obtained.Detection limit (3S/N) of the method was 0.093 mg·kg-1.Tests for recovery and precision were made by addition of 1.0,2.0,3.0 μg·L-1 of standard cobalt solution to 3 different health-care food samples,and determined by the proposed method,values of recovery in the range of 96.9%-105.0% and values of RSD′s (n=7) less than 2.1% were obtained.