The sluggish redox kinetics and dissolution of polyselenide result in severe capacity attenuation of lithium-selenium (Li-Se) batteries, thus significantly limiting its practical application. In this study, we developed a facile annealing procedure to prepare CoSe2-porous carbon composites (CoSe2-PC) as a high-performance cathode material. The formation of CoSe2 nanoparticles in the carbon matrix was confirmed by high resolution transmission electron spectroscopy (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. Se@CoSe2-PC achieved a reversible capacity up to 408 mAh·g−1 after 100 charge-discharge cycles at the current rate of 1 C, a performance much higher than that of porous carbon alone. The catalytic effect of CoSe2 on the redox reaction dynamics of polyselenide was examined by cyclic voltammetric measurements using a symmetrical cell of Se@CoSe2-PC in the presence and absence of the polyselenide in the electrolyte, and this likely accounts for the high specific capacity and superior cycle performance of Se@CoSe2-PC based Li-Se batteries. Results from this work may open up a door for suppressing the dissolution of polyselenide and eventually realize Li-Se batteries of high capacity and cycle stability.