Display omitted •This is a theoretical study on growth pattern of small Pt clusters on penta-B2C.•Pt1, Pt2 and Pt4 clusters, especially Pt1, have high stability on penta-B2C.•Stable Ptn on penta-B2C are potential catalysts with Ptn as main active sites.•The system of Pt1 on penta-B2C preferably catalyzes reduction.•O2 molecules can be activated on Pt1, Pt2 and Pt4 clusters on penta-B2C. Using dispersion-corrected density functional theory (DFT-D), we systematically investigated the growth pattern of small platinum (Pt) clusters on pentagonal B2C (penta-B2C). Firstly we calculated the bonding energy of the single Pt atoms on (2 × 2), (3 × 3) and (4 × 4) penta-B2C supercells, and chose (3 × 3) penta-B2C for the subsequent simulations. Secondly we confirmed that the single Pt atom on penta-B2C is stable. And then we stepwise investigated the growth pattern of Pt clusters. The result indicates that the Pt1, Pt2 and Pt4 clusters on penta-B2C are stable, and the single Pt atom on penta-B2C is the most stable structure. Based on the analysis of the electronic structure and the frontier molecular orbitals, the Pt1, Pt2 and Pt4 clusters on penta-B2C have the potential to be used as the efficient catalysts.