Without presence of high molecular weight capping agents, tiny Pt nanoparticles (<3 nm) are prone to agglomeration due to Oswald ripening. However, the use of capping agents will block the active sites of Pt nanoparticles, making them catalytically inefficient in polymer electrolyte membrane fuel cells. In this work, we have developed a modified citrate reduction method assisted by inorganic salt stabilization for the preparation of very stable and highly dispersed Pt hydrosols (2.0 nm). The addition of inorganic salt (stabilizing Pt hydrosols through a thicker electrostatic double layer) significantly reduces the citrate amount (Cyt(3-)/Pt4+ = 1:1), therefore the conventionally used post heat treatment to remove excess citrate is unnecessary for carbon supported Pt electrocatalysts. The open circuit potentials of the Pt precursors are measured, and most probably the first time used to account for the Pt hydrosol stability and correlated with zeta potential measurement and TEM imaging. The carbon supported Pt electrocatalysts prepared in this work exhibit high mass activity toward methanol oxidation (as a probe reaction) relative to commercially available Pt/C electrocatalysts. (C) 2014 Elsevier Ltd. All rights reserved.