To disclose the tolerant range of hydroponic Populus russkii to excessive boron and reveal the relative physiological mechanism, the present research studied the growth and physiological responses of hydroponic P. russkii to short term boron stress (1, 5, and 10 mmol/L boric acid). The results showed that: (1) the plants grew better under 1 mmol/L boric acid treatment than CK (1/2 Hoagland solution, 0.05 mmol/L boric acid). The content of leaf photosynthetic pigments, net photosynthetic rate, the activities of SOD and APX, and the content of ascorbic acid increased significantly. (2) P. russkii suffered slight stress under 5 mmol/L boric acid treatment as leaf chlorosis was observed. Compared with CK, the content of Chlb and the activities of SOD and APX increased significantly, while the Chla/Chlb ratio decreased. (3) Serious symptom (growth inhibition of shoots and roots) arose when the plants were treated with 10 mmol/L boric acid, accompanying with decrease of F_v/F_m and Chla/Chlb ratio, and increase of MDA content. The activity of POD, the contents of ascorbic acid, free proline, and soluble sugars increased significantly. The present study showed that hydroponic P. russkii can scavenge ROS effectively by upregulating the activities of antioxidant enzymes and the contents of nonenzymatic antioxidants and osmoprotectants under shortterm stress, resulting in strong tolerance ensuring the plants to grow normally under 5 mmol/L boric acid.