Previous reports show that the {1 1 1} crystal facets of Pt-based nanocrystal catalysts are highly active for the electrooxidation of methanol. In this work, platinum–silver (Pt–Ag) alloy octahedral nanocrystals with exposed {1 1 1} facets are successfully synthesized through a one-pot, wet-chemical route. The growth mechanism of octahedral nanocrystals can be attributed to the stabilization of {1 1 1} facets by PVP. The electrocatalytic performances of the Pt–Ag octahedral nanocrystals with different Pt/Ag ratio and commercial Pt/C are studied. The results show that the electrocatalytic performances of the Pt–Ag octahedral nanocrystals are much better than that of the commercial Pt/C catalyst, and the Pt–Ag octahedral nanocrystals with a Pt/Ag ratio of 2:1 show the best electrocatalytic performances among the Pt–Ag octahedral nanocrystals. The Pt–Ag octahedral nanocrystals might be a promising candidate as anode catalyst for DMFCs.