A pi-conjugated microporous poly(benzothiadiazole) (hereafter denoted as BBT) is synthesized through palladium-catalyzed Sonogashira-Hagihara cross-coupling polycondensation, and used as a novel organic semiconductor photocatalyst for both photocatalytic H-2 production and pollutant degradation under visible light (lambda > 420 nm) irradiation. Furthermore, BBT/TiO2 heterojunction is conveniently fabricated through an in-situ polycondensation procedure of 4,7-dibromobenzo[c][1,2,5]thiadiazole and 1,3,5-triethynylbenzene in the presence of commercial TiO2. After optimizing the composition ratio, the resultant BBT/TiO2 heterojunction exhibited dramatically enhanced visible-light-responsive photocatalytic activities (similar to 18.0 and 20.4 times higher activity for H2 evolution and ciprofloxacin degradation, respectively) as compared BBT alone. Detailed investigations revealed that the BBT/TiO2 heterojunction interface can accelerate the photogenerated electron transferring from BBT to TiO2, and then improve the photoactivity. The present work exhibits some interesting points and dramatic improvement of photoactivity when an organic semiconductor is combined with an inorganic one, which provides a novel direction to exploit and fabricate photocatalyst for solar energy conversion and pollutant degradation. (C) 2016 Elsevier B.V. All rights reserved.