The effect of hydrogen addition on silica growth in burner-stabilized methane/air flames with trace amounts of hexamethyldisiloxane are reported. Profiles of the aggregates' radius of gyration R-g and monomer radius a versus residence time were measured by laser light scattering. Experiments were performed at equivalence ratios of 0.8, 1.0 and 1.3, with mole fractions of 0-0.4 of hydrogen in the fuel. At equal mass flux, the addition of hydrogen was found to result in decreasing R-g and a. However, keeping the flame temperature rather than the mass flux constant upon hydrogen addition resulted in the same measured profiles. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.