The growth characteristics of Paeonia ostii ‘Fengdan’ seedlings roots in response to trichokonins-spray treatment were investigated in this study. One-year-old seedlings of P. ostii ‘Fengdan’ were potted in plastic cups containing garden mold and grown under field conditions. The results showed that application of trichokonins significantly promoted root growth in P. ostii ‘Fengdan’ seedlings. The total root projection area, total root surface area, total root volume, total root length, root number and root diameter of seedlings treated with 0.25 mg/L trichokonins were higher by 141.70, 116.59, 119.44, 55.97, 348.88 and 127.78%, respectively, than that of the control. Thus, the results supported the hypothesis that good growth condition for roots could directly improve their nutrient absorption and utilization efficiency, promoting plant growth and development.