Abstract: Abstract Objective: To establish an accurate, simple, cheap, efficient and promotable biological assay for serum folate. Methods: Based on the property of folate for growth of lactobacillus, serum folate test method was established by use of acticarbon powder adsorption of organic impurities in the test water. Results: The measure range was 0 ～ 0.6μg / L and the detection limit was 0.017μg / L. The intra and inter CVs were less than 5% and the recovery rate was 98.1 % ～102.4%. The correlation coefficient was 0.963 comparing with chemiluminescence method. The reagent could be stable more than 6 months when frozen at -20 ℃. Conclusion: This serum folate test method was accurate, simple, cheap, efficient,promotable, and applicable to the screening for the large samples.