Microalgae are widely studied for biofuel production, however, current technologies to harvest microalgae for this purpose are not well developed. In this work, a bacterial strain W01 was isolated from activated sludge and identified as Solibacillus silvestris. Bioflocculant in the culture broth of W01 showed 90% flocculating efficiency on marine microalga Nannochloropsis oceanica, and no metal ion was required for the flocculation process. Chemical analysis of the purified bioflocculant indicated that it is a proteoglycan composed of 75.1% carbohydrate and 24.9% protein (w/w). The bioflocculant exhibits no effect on the growth of microalgal cells and can be reused to for economical harvesting of N. oceanica. This is the first report that strain of S. silvestris can produce bioflocculant for microalgae harvest. The novel bioflocculant produced by W01 has the potential to harvest marine microalgae for cost-effective production of microalgal bioproducts. (C) 2012 Elsevier Ltd. All rights reserved.