This study reports the electrocatalytic activity of alloyed Pt_10−x–Fe_x/CNTs (x = 1, 2, 3, 4, 5) and Pt/CNTs nanoparticles. These materials were synthesized using the Brust–Schiffrin method and were tested as potential anodic electrocatalysts in a direct methanol fuel cell (DMFC). SEM, EDS, XRD, TEM and TGA studies were performed to confirm the formation of Pt–Fe alloyed nanoparticles. The nanoalloys material supported on CNTs showed a volcano-type behavior for methanol electro-oxidation when varying the relative Fe:Pt stoichiometry. An enhancement of electrocatalytic activity was observed for alloyed nanoparticles with Fe:Pt ⩽3:7 ratios. This effect was attributed to a rearrangement of the electronic structure of the Pt nanoparticles surface induced by Fe atoms. On the other hand, high Fe:Pt ratios (⩾4:6) led to depleted activities caused by a decrease of the methanol dehydrogenation process on the alloyed nanoparticles surface. Cyclic voltammetry and chronoamperometry measurements indicated that a ratio of Fe:Pt = 3:7 is the optimum to obtain the best electrocatalytic activity on CNTs-supported alloyed nanoparticles for methanol oxidation reaction.