The design of porous bimetallic nanocrystals (NCs) is very important for electrochemical energy conversion. Herein, we report an aqueous solution method for one-step fabrication of porous PtCu NCs assembled by spatially interconnected arms in high yield by a simple ultrasonic treatment of the reaction mixture at room temperature. The proposed method, without the need for multi-step synthesis, high temperatures, and organic solvents, shows an obvious advantage of simplicity for the feasible synthesis of bimetallic PtCu NCs with a porous structure. The as-made porous PtCu NCs are highly active and durable catalysts for the methanol oxidation reaction due to their porous structure and bimetallic composition.