This experiment aimed to study the effects of cold stress on root growth and related physiological characteristics in two sugarcane varieties with different cold resistance.The roots of sugarcane seedlings of cold-resistant variety GT28 and cold-susceptible variety ROC22 derived from water culture were used as the plant materials.Two treatments were performed at 25 C as control and 4 C as cold stress,respectively.Morphological growth characteristics and physiological characteristics,including root length,root volume,root microstructure,activities of root vigor,superoxide dismutase(SOD)and peroxidase(POD),contents of malondialdehyde(MDA),proline,soluble sugar,and soluble protein were measured.The results showed that as the root growth was inhibited under cold stress,the average root length and root volume were decreased in the cold treatment as compared to the control,and the decreases were less in GT28 than in ROC22.After 3 days of cold stress,the root microstructure was changed as getting swelling and deformed,and disorder of cellular structure was observed in both varieties; however,the root deformation was much significant in the cold-susceptible variety of ROC22 than in the cold-resistant variety of GT28.As the cold stress prolonged,the activities of root vigor were significantly decreased in both sugarcane varieties,but it decreased more obviously in ROC22 than in GT28.The contents of MDA,proline,soluble sugar,soluble protein,and the activities of POD and SOD were higher in cold treatments than in control.Compared to variety of ROC22,the contents of soluble sugar and proline and the activities of POD and SOD were higher in GT28.The results indicated that cold resistance/susceptibility is variety dependent in sugarcane.