Plasmonic nanostructures of semiconductors and noble metal nanospheres (NSs) hold great promise in the applications of solar energy conversion. Although it is known that the size of NSs plays a critical role in determining the photocatalytic performance of the resultant nanohybrids, the actual effects depend on multiple variables and needs to be elucidated for each specific scenario. Herein, ZnO nanorods (NRs) modified with AuNSs of diameters varying from 20 to 80 nm have been prepared to investigate the size effect of AuNSs on the photocatalytic activity of Au-ZnO hybrids. Interestingly, the Au-ZnONRs with 40nm AuNSs demonstrate higher photocatalytic activity than the nanohybrids with AuNSs of either smaller or larger sizes. A possible "trade-off" mechanism between efficient charge transfer for smaller NSs and stronger LSPR effect for larger ones is proposed. (C) 2017 Elsevier Inc. All rights reserved.