Poly(gamma-glutamic acid) (gamma-PGA) prepared from a culture of Bacillus subtilis had a high flocculating activity and its flocculation properties mere investigated. Flocculating activity of gamma-PGA in a kaolin suspension was stimulated by the addition of Ca2+, Mg2+ or Fe2+ to the suspension. High flocculating activity of gamma-PGA was induced in a kaolin suspension by addition of Fe3+ or Al3+ and pH adjustment to the neutral range. Various inorganic suspensions of active carbon, acid clay, solid soil, and calcium and magnesium compounds mere flocculated by gamma-PGA. Flocculation of organic suspensions such as cellulose and yeast by gamma-PGA occurred when Fe2+, Fe3+ or Al3+ mere added and the pHs of the suspensions were adjusted to the neutral range. From these flocculation properties in various suspensions, it may be possible to use gamma-PGA as a new biodegradable, harmless biopolymer flocculant.