Fuel cells are highly efficient conversion devices to alleviate energy crisis and environmental pollution, but still encounter technical challenges to further improve catalytic efficiency of Pt-based electrocatalysts. In this work, PtNi multi-branched nanostructures (PtNi MBNs) were successfully prepared by a simple and economical one-step solvothermal method. The average diameter of the branches is about 9 nm, with numerous atom steps and Pt-rich surface. The prepared electrocatalyst shows excellent bifunctionality in acidic electrolytes, catalyzing both oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). The half-wave potential of 0.966 V for ORR is much higher than that of commercial Pt/C (0.931 V), and only decreases 14 mV after 8,000 cycles. For MOR, the specific activity of PtNi MBNs is 18.1 A m-2 Pt, better than that of commercial Pt/C (7.8 A m-2 Pt), indicating an optimal intrinsic activity. The remarkable bifunctionality of PtNi MBNs is attributed to the exposed electrochemical surface area, abundant atomic steps, and Pt-rich surface provided by the unique multi-branched nanostructure. This facile preparation technique offers a promising application for designing high-performance electrocatalyst for acid direct methanol fuel cell in the future.