Glutamate synthase (GOGAT)is a key enzyme in glutamine synthetase (GS)/GOGAT cycle and at the hub of carbon and nitrogen metabolism, catalyzing the formation of glutamate from ?-oxoglutarate and glutamine. In this study, members of GOGAT family in Populus trichocarpa were identified and analyzed by bioinformatics. The four PtGOGATs were divided into two subgroups: subgroup A (Fd-GOGAT1 and Fd-GOGAT2)and subgroup B (NADH-GOGAT1 and NADH-GOGAT2). Many important elements have been identified in the promoters of different PtGOGATs, including hormone- and light-responsive elements. Meanwhile, the transcript levels of PxGOGATs were affected by light and diurnal cycle. Quantitative real-time PCR showed PxFd-GOGATs and PxNADH-GOGATs were mainly expressed in leaves and roots in Populus × xiaohei T. S. Hwang et Liang, respectively. Under elevated CO2, PxGOGATs were suppressed in all tissues except the stem. And PxFd-GOGATs and PxNADH-GOGATs were strongly induced by nitrogen in leaves and roots, respectively. In addition, PxGOGATs were stimulated significantly in roots in response to NH4+and glutamine directly. Our results provide new insights about GOGATs in poplar and their expression patterns under exogenous substances, to lay molecular basis for studying gene function and provide a reference for exploring putative roles of GOGATs in carbon-nitrogen balance.