Abstract Colloidal metal and their alloys nanoparticles have been found to potentially offer exceptional catalytic activity. Many researchers have worked to tailor the shape, size, and atomic composition of Au-based bimetallic nanocrystals to enhance their catalytic activity. However, the study of free colloidal anisotropic Au-based particles as catalyst of hydrogenation process is still limited. Here, we evaluated the bimetallic gold-silver (AuAg) mesoflowers (MFs) with sharp tips as a catalyst for hydrogenation of acetone to isopropanol under microwave radiation. The shape and size of the branched MFs was adjusted by controlling the addition of AgNO3 precursor. The resulting AuAg MFs were found to have higher catalytic activity than monometallic Au mesoparticles (Au MPs). The degradation rate of acetone without a catalyst is ±46%, while the degradation rate of acetone in the presence of Au MPs and AuAg MFs catalysts is ±66%, and ±71%, respectively. These correspond to the turn over number (TON) and turn over frequency (TOF) values of approximately 1827 and 9.1 s−1, respectively, for the AuAg MFs. This is significantly higher compared to the TON and TOF values for Au MPs, i.e. 746 and 3.7 s−1, respectively. High electron density on their sharp tips and the presence of Ag atoms on the AuAg alloy surface may be the key points in enhancing the chemical reaction with the oxygen atom in the C═O bond and generates a surface-hydrogen species to form isopropanol molecules.