As a novel material for water depollution, conjugated polydiphenylbutadiyne (PDPB) nanofibers have received attention due to their visible light responsive photocatalytic activity. In this study, we successfully prepared a PDPB/SnO₂ p–n heterojunction by an in situ growth route. The XPS characterization indicates the generation of Sn–C bonds between SnO₂ and PDPB, which would decrease the bandgap of SnO₂ and promote the transference efficiency of electrons and holes between these two components. The PDPB could act as the sensitizer to enlarge the solar light absorption region of the heterojunction. The SnO₂ provides a stable mesoporous structure and enhanced hydrophilic properties. The solar-driven photodegradation rate of Rhodamine B over the PDPB/SnO₂ (ratio is 2 : 1) is 4 times higher than that of the pure SnO₂ and 2 times higher than that of the pure PDPB nanofibers. Our strategy gives a facile strategy for the preparation of an organic–inorganic hybrid heterojunction with high solar light activity.