Photocatalytic hydrogel composites were prepared by using multifunctional microporous polymer particles as a reinforcing agent and also as a catalytic species. A benzothiadiazole-based conjugated microporous polymer (BTCMP) was synthesized by the Sonogashira-Hagihara reaction between 4,7-dibromo-2,1,3-benzothiadiazole and 1,3,5-triethynylbenzene as insoluble particles. BTCMP particles were functionalized with acryl groups via the thiol-yne click reaction with 2-aminoethanethiol and subsequent reaction with acryloyl chloride. Acrylated BTCMP particles were polymerized with acrylamide in a glass mold to yield a highly elastic hydrogel composite sheet. The tensile test results showed that covalently incorporated BTCMP particles significantly enhanced the mechanical properties of the hydrogels compared with a pure polyacrylamide hydrogel. A possible application of the hydrogel composites for the removal of a dye in water was studied using methylene blue as an exemplary dye. The maximum methylene blue adsorption capacity of the hydrogel composite containing 2 wt% of BTCMP particles was 2.6 times higher than that of the pure polyacrylamide hydrogel. The hydrogel composite with photocatalytic activity originated from benzothiadiazole groups degraded adsorbed methylene blue molecules in an aqueous solution upon UV irradiation. The hydrogel composite could be reused for the methylene blue removal without any significant decrease in adsorption capacity and catalytic activity.