Abstract: OBJECTIVE To explore a method to determine the folic acid content in medicament and foods by bioassay, to resolve the problem that folic acid content of foods can’t be determined by HPLC, and to provide a way to calculate the ingestion of folic acid per day for pregnant woman. METHODS Utilizing the growth of Lactobacillus Casei (L.C) depending on folic acid to determine bacterial suspension’s absorbency, the content of folic acid is obtained. RESULTS Through examining three kinds of samples, the coefficient variations of within-run, between-run and the rate of recovery have been got, and the result of the HPLC’s was compared. CONCLUSION Bioassay is more stable and applicable than HPLC.