Platinum nanocrystals (Pt NCs) have excellent catalytic activity toward oxygen reduction reaction (ORR). The morphology (e.g. size, facet, shape) of Pt NCs will change upon heating and the effect of this change in morphology on ORR activities of Pt NCs is unclear. In this work, the effects of heat treatment temperature and atmosphere on ORR activities of catalysts Pt NCs supported on carbon nanotubes were studied. Pt NCs were synthesized via a homogeneous aqueous chemical reduction method and then were dispersed and adsorbed onto carbon nanotubes support. It was found that after heat treatment at 300 degrees C, the Pt NCs have larger active surface areas, higher activity and longer durability toward ORR. And when the heat treatment was conducted in atmosphere of 20%H-2-80%Ar (by volume), the catalysts had higher ORR activity than that heated in pure Ar gas. This work demonstrated that Pt NCs after heat treatment in a suitable atmosphere will cause a fine tuning of the surface atomic configuration, which determine the activity and long-term durability of Pt NCs catalysts. (C) 2014 Elsevier B.V. All rights reserved.