Nanostructured Pt-metal alloys have shown impressive catalytic properties for the oxygen reduction reaction (ORR) in acidic medium, but their long-term stability has not been satisfactory. Herein, we look beyond the traditional Pt-metal alloys and have developed a new kind of Pt-nonmetal alloy electrocatalyst for the ORR. Specifically, the novel catalyst is composed of interconnected platinum monophosphide (PtP) alloy nanocrystals (∼3-4 nm) and featured supportless nanotube array morphologies. Due to the unique combination of composition and structure, the obtained PtP alloy nanotube arrays not only exhibited remarkable ORR activity, but also showed almost no degradation of the half-wave potential after accelerated durability tests. The result suggests that alloying Pt with a nonmetallic element (such as P) is indeed an effective approach to address the poor stability of Pt-based catalysts in acidic medium.