FST, also known as Follistatin, is a single-chain gonadal protein that specifically inhibits follicle-stimulating hormone release. The single FST gene encodes two isoforms, FST317 and FST344 containing 317 and 344 amino acids respectively, resulting from alternative splicing of the precursor mRNA. Recombinant human FST, fused to His-tag at C-terminus, was expressed in Sf9 and purified by using conventional chromatography techniques.