Proton transport played a crucial part in the fuel cells, sensors, and batteries. The electrolyte used in fuel cells should possess high proton conductivity and good chemical stability. Herein, taking advantage of the high proton conductivity of metal-organic framework (MOF) and the good chemical stability of branched polymers, a new heterometallic mediated MOF (Zr-Cr-SO3H) is synthesized and utilized as a filler in the highly branched sulfonated polymer (BSP). In addition, Zr-SO3H MOF is also prepared for comparison. Transmission electron microscope study shows that the prepared MOF particles are spherical in size and interconnected through nanosheets. The optimized quantity of MOFs inside the polymer matrix improves the water sorption, mechanical property, and proton conductivity. The composite membranes display an improved open-circuit voltage than the pristine BSP membrane. By comparing the Zr-SO3H MOF incorporated composite membrane, Zr-Cr-SO3H MOF incorporated composite membranes display higher proton conductivity and peak power density in a single-cell test. In particular, the single-cell fabricated with Zr-Cr-SO3H MOF incorporated composite membrane is able to reach the peak power density of 64.6 mWcm(-2) at 60 degrees C, which is 26% greater than the Nafion 212 membrane. Furthermore, this work offers a new strategy for the utilization of hetero-metal MOF as a filler for proton exchange membrane applications.