The outstanding performance of halide perovskites in optoelectronic applications can be partly attributed to their high absorption coefficient and long carrier lifetime, which are also desirable for photocatalysts. Herein, we report that cesium lead iodide perovskite quantum dots (CsPbI3 QDs) can be used as catalysts to promote the polymerization of 2,2′,5′,2″-ter-3,4-ethylenedioxythiophene under visible light illumination while preserving the quantum dot in the desirable cubic crystal phase. Simultaneously, the generated conducting poly­(3,4-ethylenedioxythiophene), PEDOT, encapsulates and stabilizes the morphology of the CsPbI3 QDs. The photocatalytic polymerization clearly depends on the concentration of the CsPbI3 QDs, and the CsPbI3 QDs maintain the desirable perovskite phase when the concentration of the QD increases. Molecular oxygen and 1,4-benzoquinone can serve as electron acceptors during the photocatalytic polymerization reaction. When molecular oxygen is used, the structure of the CsPbI3 QD transforms from cubic to orthorhombic, while usage of 1,4-benzoquinone preserves the cubic phase of CsPbI3 QD. This novel approach enables the one-step formation of CsPbI3/PEDOT composite, which could be promising for the preparation of novel optoelectronic materials and high performance devices.