In this study, the solar photothermal conversion performance of bimetallic Au-Ag nanoparticles (NPs) was investigated experimentally. NPs were prepared using a sodium citrate thermal reduction method, using the same procedure and materials to maintain the same particle surface properties. NPs with a tunable plasmon resonance wavelength and demonstrating a high intensity in the visible region were obtained by adjusting the molar ratio of Ag to Au precursors. Experimental results show that blended Au-Ag NPs exhibit a solar photothermal conversion efficiency of 31.41%, which lies between the values of pure Au and Ag NPs under the same NP volume fraction due to the independently scatter light of the Au and Ag NPs in this composite system. Bimetallic Au-Ag NPs demonstrated the highest solar photothermal conversion efficiency of 41.37%, a 31.7% increase over that of blended Au-Ag NPs. The efficiency of the bimetallic Au-Ag NP system was also higher than that of the pure Au NPs (37.81%) with a 40% decrease in Au consumption. (C) 2017 Elsevier Ltd. All rights reserved.