Abstract: Populus alba×P. glandulosa (‘84K’) was used to study changes in photosynthetic physiological characteristics after drought stress and rehydration. Results showed that the main photosynthetic processes of ‘84K’ were not synchronous during drought stress and rehydration. During drought, the carboxylation rate, stomatal conductance (G_s), and mesophyll conductance (G_m) of ‘84K’ declined significantly, but the former decreased less than the latter two. Thus, at this time, photosynthesis was mainly restricted by G_s and G_m. After rehydration, G_m recovered rapidly; however, the photochemical quenching process and carboxylation rate did not recover to the control level, which may restrict the carbon fixation and photosynthesis of ‘84K’.