gamma-Poly(glutamic acid) (gamma-PGA), which is produced by Bacillus subtilis, was sulfonated using 2-aminoethane-1-sulfonic acid (taurine) in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (WSC) to give sulfonated gamma-PGA (gamma-PGA-sulfonate). From (1)H NMR spectroscopy and IR spectroscopy, it was confirmed that taurine was introduced to the side chain of gamma-PGA via an amide linkage. By altering the synthetic conditions, it was possible to control the content of sulfonate in gamma-PGA-sulfonate. Anticoagulant activity was investigated in order to evaluate the biological activity of gamma-PGA-sulfonate by the Lee-White test. The clotting time was prolonged when the concentration of gamma-PGA-sulfonate on the degree of sulfonation was increased. It becomes clear that gamma-PGA-sulfonate is potentially useful for various medical applications, such as drug delivery, tissue engineering, and medical materials.