By mimicking natural photosynthesis, generating hydrogen through visible-light-driven splitting of water would be an almost ideal process for converting abundant solar energy into a usable fuel in an environmentally friendly and high-energy-density manner. In a search for efficient photocatalysts that mimic such a function, here we describe a series of cycloplatinated polymer dots (Pdots), in which the platinum complex unit is presynthesized as a comonomer and then covalently linked to a conjugated polymer backbone through Suzuki-Miyaura cross-coupling polymerization. On the basis of our design strategy, the hydrogen evolution rate (HER) of the cycloplatinated Pdots can be enhanced by 12 times in comparison to that of pristine Pdots under otherwise identical conditions. In comparison to the Pt-complex-blended counterpart Pdots, the HER of cycloplatinated Pdots is over 2 times higher than that of physically blended Pdots. Furthermore, enhancement of the photocatalytic reaction time with high eventual hydrogen production and low efficiency rolloff are observed by utilizing the cycloplatinated Pdots as photocatalysts. On the basis of their performance, our cyclometallic Pdot systems appear to be alternative types of promising photocatalysts for visible-light-driven hydrogen evolution.