Platinum (Pt) decorated carbon nanotubes (CNTs) nanocatalysts (Pt/CNTs) were successfully prepared by an atomic layer deposition (ALD) method. Increased ratios of D to G band with increasing ALD cycles in Raman spectra suggested an interaction between Pt nanoparticles (NPs) and CNTs as well as increased Pt loadings. The absence of the Pt peaks in XRD before and after thermal annealing treatment demonstrated an ultra-small Pt NPs size. TEM revealed a perfect distribution of the ultra-small Pt NPs on the tube wall surface with different ALD cycles and an agglomeration of Pt NPs was observed when increasing the annealing temperature. Increased peak current density (jp) values in CV (25 cycles, denoted as Pt/CNTs-25C, 40.89 mA/mgPt, 50 cycles, Pt/CNTs-50C, 667.6 mA/mgPt and 100 cycles, Pt/CNTs-100C, 1205.7 mA/mgPt) were obtained toward the methanol oxidation reaction (MOR) with increasing the ALD cycles. 100 and 300 degrees C hydrogen annealed Pt/CNTs-50C (denoted as Pt/CNTs-50C-100A and Pt/CNTs-50C-300A) gave increased and decreased j(p) values (1200 and 800 mA/mgPt) due to the positive hydrogen reduction of Pt(II)/Pt(IV) species and the negative Pt NPs agglomeration. Pt/CNTs-100C-100A exhibited the highest j(p) value (2000 mA/mgPt) after applying the optimal 100 degrees C annealing treatment, enabling it an excellent candidate for MOR application. (C) The Author(s) 2015. Published by ECS.