The presence of low concentration of inosine in solution in soil has increased the root growth as shown in our previous work. Thus the aim of this work was to clear the mechanism of the inosine-induced enhancement of root growth with emphasis on plant hormone and metabolites profile. In the first experiment the rice plant (Oryza sativa L. cv Nipponbare) was precultivated in nutrient solution for 3 weeks. Then seedlings with the same size were transferred to pots with the following treatment solutions (0 N + 0 inosine, 0 N + 20 mg L-1 inosine, 4 mg L-1 N + 0 inosine and 4 mg L-1 N + 20 mg L-1 inosine). Two weeks after the treatment started, xylem sap was collected for determining cytokinin and auxin concentration by ELISA, then fresh and dry weight of shoot and root, and root length were measured. In the second experiment, rice seedling were prepared as Experiment 1 then samples were collected after inosine treatment (0, 1, 2, 24, 72, and 96 hours) for the analysis of metabolites profiling by using GC-MS. Dry weight (shoot and root), and root length and number of lateral root were measured. As a result, inosine application increased root length and concentrations of trans-zeatin riboside and indole-3-acetic acid content in xylem sap significantly. The allantoin was the most up regulated compound in the metabolite profile. Thus, it is suggested that inosine application increased concentration of plant hormones and allantoin, possibly resulting in growth enhancement of plant root.