Polythiophene (PT)/Bi2MoO6 nanocomposites were synthesized by an in situ chemical oxidative polymerization method. The photo-degradation of a typical model pollutant, rhodamine B (RhB) under visible-light irradiation (lambda > 420 nm), demonstrated that the PT/Bi2MoO6 composite showed higher photocatalytic activity than bare Bi2MoO6. The good performance of the PT/Bi2MoO6 composite could be attributed to the high separation efficiency of the photo-generated charge carriers contributed by the synergic effect between PT and Bi2MoO6, as well as the high charge transfer rate due to the hole transporting ability of PT. The results may provide some insights into the design and development of other effective polymer-semiconductor photocatalysts for pollutant degradation under sunlight irradiation.