Abstract SnO2 and Pt nanoparticles were deposited on nitrogen-doped CNT (CNx) in sequence to construct a Pt–SnO2/CNx hybrid electrocatalyst for proton-exchange membrane fuel cells (PEMFC). Crystalline and amorphous SnO2 were deposited selectively by controlling the temperature via atomic layer deposition method. The electrochemical stability of Pt catalyst was enhanced with the addition of SnO2, as demonstrated by accelerated durability tests. Furthermore, the crystalline SnO2 was more effective than the amorphous counterpart in stabilizing the Pt catalysts. The enhanced electrochemical stability resulted from the addition of SnO2 was explained by the interaction between Pt and SnO2. Crystalline SnO2 also increased the electrochemical surface area of Pt catalysts, resulting in higher activity.