We report a simple approach to fabricate aligned bimetallic Pt–Cu microwires with a three-dimensional nanoporous structure, tunable composition, and high catalytic activity by dealloying a dilute Pt3Cu97 precursor. Each microwire possesses inherent ultrafine nanoporous structure with uniformly distributed Pt–Cu alloy ligaments and nanopores with a dimension of ∼2 nm. Electrochemical measurements manifest that the nanoporous Pt–Cu microwires have significantly enhanced electrocatalytic activities compared with a commercial Pt/C nanoparticulate catalyst. With evident advantages of facile preparation and enhanced catalytic performance together with low material costs, the nanoporous Pt–Cu microwires hold great promise as a high-performance catalyst for electrochemical energy conversion.