A variety of surface waters used for drinking water sources were collected from different parts of Japan to investigate a correlation between the concentration of hydrophilic biopolymer (e.g. proteins and polysaccharides) in the feed water and membrane fouling in microfiltration. Hollow-fiber membranes made from polyvinylidene fluoride with a nominal pore size of 0.1 μm were used in the series of experiments involving the constant-flow mode of operation with automatic periodical backwashing. Easily available indexes of water quality, such as dissolved organic carbon, UV absorbance, Ca concentration and turbidity could not explain the degree of fouling encountered in the filtration tests. In contrast, a clear correlation between the concentrations of biopolymers determined by liquid chromatography with organic carbon detection (LC-OCD) and membrane fouling was confirmed in this study. The concentrations of humics exhibited a weak correlation. The impacts of seasonal variation of feed water and coagulant dosage on membrane fouling were also explained well by biopolymer concentrations. Concentrations of biopolymers can be a useful indicator of the fouling potential of feed water in microfiltration.