Folic acid (FA) affect human physiology and drug metabolism. Up to now, the effect of microgravity on the pharmacokinetics of FA remains unclear. The pharmacokinetics of FA in Sprague-Dawley (SD) rats are laying a foundation for safe medicine administration of astronauts. Proteins expression of such FA metabolic enzymes as Methyltetrahydrofolate reductase (MTHFR), Cystathionine beta synthase (CBS) and Methionine synthase (MS) in a variety of organs was analyzed with Western-Blot, and mRNA expression was detected by RT-PCR. The plasma concentration-time profile of FA in normal or tail-suspended SD rats was acquired by liquid chromatography-tandem mass spectrometry (LC-MS/MS) after oral administration of FA. Area under curve (AUC) and Cmax of FA in SD rats decreased significantly with extending period of tail-suspension. In terms of expressed level of metabolic enzymes over four suspension terms, as well as the level of the corresponding mRNAs, the following regularities were found: an obvious sharp decline of MTHFR tissue in kidney, a time-dependent increase of CBS in liver tissue and duodenum tissues, the resemblance of MS fluctuation to that of CBS in tested tissues. A four-week simulated microgravity of SD rats exhibits an unequivocal diminish of bioavailability of FA, and simulated microgravity shows a varying effect on the expression of FA-metabolizing enzyme in a variety of tissues.