Utilized as an oxygen reduction reaction (ORR) catalyst for magnesium-air battery, multi-walled carbon nanotubes (MWCNTs) supported PdSn bimetallic catalyst was synthesized by a facile borohydride reduction method. Heat-treatment was applied to improve the catalytic activity and stability by tailoring the alloying content and surface components of the catalyst. Results illustrated that the 24 h heat-treated PdSn/MWCNTs exhibited best alkaline ORR performance with low over-potential, high diffusion-limited current density and superior stability. A magnesium-air battery employing the 24 h heat-treated PdSn/MWCNTs as cathodic catalyst showed higher discharging power density and enhanced durability compared with those employing the unheated sample and commercial Pd/C catalyst.