Abstract: Folic acid is an essential nutrient for the growth of Lactobacillus rhamnosus,The microbial assay of folic acid was established by using the correlation between the growth rate of Lactobacillus rhamnosus and the content of folic acid.In view of the long test cycle of microbial method and the cumbersome preservation of bacteria,this method is based on the method of GB 5009.211-2014 National Food Safety Standard Determination of Folic acid in Food,improving the preparation method of lactobacillus inoculant and the culture time of folic acid culture liquid.This paper verified the applicability of the optimization method by analyzing the linearity of the standard curve,precision,accuracy and stability of the method．This method has good curve relation （R² > 0.99）,good recovery > 90%,good precision and accuracy,simple operation,shortens test period,improves detection efficiency,and provides a basis for improving the detection method of folic acid．

Key words: folic acid, test period, linear, precision, accuracy