Three-dimensional porous PtNi hollow nanochains are successfully synthesized via galvanic replacement method using Ni nanosponges as sacrificial templates in an aqueous solution. It is found that the composition and shell thickness of the 3D PtNi hollow nanochains can be easily controlled by tuning the concentration of Pt precursors. The as-prepared PtNi hollow nanochains with optimized composition present high electrochemical surface area (70.8 m2 g-1), which is close to that of commercial Pt/C (83 m2 g-1). Moreover, the PtNi catalyst with Pt content of ~77% presents superior electrocatalytic performance for oxygen reduction reaction compared to commercial Pt/C. It shows a mass activity of 0.58 A mgPt-1, which is around 3 times higher than that of Pt/C. This strategy may be extended to the preparation of other multimetallic nanocrystals with 3D hollow nanostructures, which are expected to present high catalytic properties.