Platinum nanoparticles supported on multiwalled carbon nanotubes (Pt/MWCNT) were prepared using controlled electrochemical deposition from Ar-saturated H 2 PtCl 6 solution. The electrodeposition parameters were varied to observe change in the surface morphology and electrocatalytic activity of the Pt/MWCNT catalysts for oxygen reduction reaction (ORR). Surface morphology of the prepared catalysts was studied by scanning electron microscope (SEM) and scanning transmission electron microscope (STEM). For electrochemical characterization of the Pt/MWCNT electrocatalysts, CO-stripping and cyclic voltammetry (CV) experiments were performed in 0.05 M H 2 SO 4 solution. The ORR was studied in acid medium using the rotating disk electrode (RDE) method. The results obtained were analyzed and compared to those of commercial Pt/C. The size, shape and distribution of Pt particles as well as the electrochemical behavior of Pt/MWCNT modified electrodes showed strong dependence on the deposition parameters. The catalyst materials prepared by electrochemical deposition showed higher specific activities than commercial Pt/C catalyst. The Pt/MWCNT cathode materials showed remarkable stability during repetitive potential cycling in 0. Proton exchange membrane fuel cell (PEMFC) is identified as one of the most promising environmentally friendly sustainable energy conversion devices that efficiently convert fuel energy into electricity through electrochemical processes. [1][2][3] In comparison to the conventional internal combustion engine, low-temperature fuel cells are preferred for energy conversion in vehicles because of its green operating system, high efficiency and renewable energy resources.4,5 One of the most critical challenges for commercializing fuel cells is the development of more efficient, highly active and durable electrocatalysts to improve the sluggish kinetics of the oxygen reduction reaction (ORR). To date, Pt-based cathode catalysts have shown significantly high electrocatalytic activity toward the ORR as compared to other metals, alloys, core-shell structures, mixed metal oxides and nonnoble metal catalysts.6-15 Considerable efforts have been dedicated to minimize the amount of Pt loading and improve its electrocatalytic activity and durability, mainly because of its scarcity and high cost. [16][17][18][19]