Aims: The aims of the study were to identify the effects of rice endophyte Pantoea agglomerans YS19 on host plant growth and allocations of photosynthates. Methods and Results: Endophytic diazotrophic YS19 showed nitrogen-fixing activity in N-free medium, and produced four categories of phytohormones which were indole-3-acetic acid, abscisic acid, gibberellic acid and cytokinin in Luria-Bertani medium. Inoculation of YS19 improved the biomass of the 12-day-cultivated host rice seedlings by 63.4% on N-free medium or by 18.7% on N-supplemented medium. Spraying of YS19 cell culture onto the rice plants at the premilk stage enhanced the transportation of the photosynthetic assimilation product from the source (flag leaves) to the sink (stachys) significantly. The formation of the plant sink was obviously inhibited when YS19 cell culture was applied at the late milk stage. Conclusions: This research suggests that endophyte YS19 promotes host rice plant growth and affects allocations of host photosynthates. Significance and Impact of the Study: These findings suggested that YS19 possesses the potential for increasing rice production in field application. Meanwhile, a suitable plant growth stage must be selected for the foliar spraying of YS19 cell culture.