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Bioflocculants like polysaccharides are excellent alternatives to harmful synthetic flocculants and usability under stricter levels of ecosystem protection. In this study, an exopolysaccharide producing strain Paenibacillus sp. M21629 was isolated. The exopolysaccharide was abundant in carboxylic groups and named floccuronic acid with a high weight average molecular weight of 2.38 × 108 Da. The hexasaccharide repeating units of floccuronic acid were →3)-α-D-Man p -(1 → 3)-4-Suc-β-D-Man p -(1 → 3)-β-D-Glc p -(1 → 4)-β-D-Glc p A-(1 → 4)[4,6-Pyr-β-D-Gal p -(1 → 3)]-β-D-Gal p -(1→. The floccuronic acid at 0.5–1 ppm showed high turbidity removal efficiency in kaolin suspension (99.8%), coal wastewater (98.8%), and high-turbidity drinking water (89.2%). The flocculation ability of floccuronic acid depended on the instability of solid particles. Owing to these encouraging results, floccuronic acid is expected to be a useful bioflocculant applied in wastewater treatment and the utilization of water resources. [Display omitted] • A Paenibacillus isolate produces the exopolysaccharide floccuronic acid with molecular weight of 2.38×108 Da. • The floccuronic acid is composed of mannose, galactose, glucose, and gluconic acid with pyruvic and succinyl substitutions. • The floccuronic acid shows high turbidity removal efficiency in several suspensions. • The bridging mechanism underpins the flocculant action of floccuronic acid. [ABSTRACT FROM AUTHOR]