Core-shell structured bimetallic platinum-metal (Pt−M) nanoparticles, as a new class of active and stable nanocatalysts, have shown many advantages in increasing the utilization of precious Pt and improving electrocatalytic performances. Here, a core-shell Pt3Co@Pt supported on porous graphitic carbon (denoted as Pt3Co@Pt/C) is synthesized via a simple thermal method, and further used as an efficient electrocatalyst for oxygen reduction reaction (ORR) in the direct methanol fuel cell. An atomic-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) measurement combining with line-profile analysis reveals that the average thickness of Pt-shell is around 0.4–0.6 nm, forming an ultrathin catalytic layer. Given its unique geometric and electronic structure, the as-prepared Pt3Co@Pt/C displays highly enhanced electrocatalytic ORR activity and stability, boosted anti-methanol poisoning ability with a high onset potential and an exceptional half-wave potential in 0.1 M HClO4 solution. Impressively, its mass activity (0.71 mA mgPt−1) and specific activity (2.75 mA cmPt−2) for ORR are 3.7- and 8.1-fold higher than those of commercial Pt/C catalyst, respectively. The Pt3Co@Pt/C nanocatalysts show remarkable tolerance against methanol poisoning, evidenced by the in situ Fourier-transform infrared (FTIR) spectroscopy. This work points out a path for the design of high-performance nanocatalysts for accelerating the development of clean energy technologies involving ORR.