Abstract: Screening of bioflocculant-producing microorganisms was carried out. A strain that secreted excellent bioflocculant was isolated from municipal sewage using the spread plate technique, identified as Klebsiella sp. by the analytical profile index (API) identification system, and named A₉. Several important factors that had an effect on A₉’s bioflocculant-producing and flocculating activity were studied. A total of 4 g/L Kaolin suspension was used to measure the flocculating activity of the bioflocculant from A₉. It was found that maltose and urea were A₉’s best carbon and nitrogen sources, respectively, and the flocculating activity of the flocculating agent from A₉ was markedly increased by the addition of trivalent cations such as Fe³⁺ and Al³⁺; furthermore, the bioflocculant produced by A₉ was most effective when the pH value was 6.0.