Cadmium (Cd) is one of major environmental pollutants mainly emanating from mining, industrial trash, anthropogenic activity and use of agro-chemicals. Even in trace concentrations, Cd can cause serious problems to all organisms. In most plant species, Cd accumulated in the roots and was mainly retained in insoluble and soluble forms. Cd inhibited root growth, damaged root hair and root tips by modifying lipid composition of root plasma membrane, increasing the levels of lipid peroxidation. However, it is still unclear about the effect of Cd on the changes in superoxide anions and phytohormone levels, antioxidative capability of CAT, APX and GR in tobacco (Nicotiana tabacum L.) roots. In the present study, the contents of superoxide anions, soluble proteins, phytohormones, the levels of antioxidative capability and lipid peroxidation in roots were determined. Tobacco seedlings with six leaves and same height were cultivated hydroponically in pots containing Hoagland′s nutrient solution. After 15d Cd(NO3)2 was added to nutrient solution at 0, 25, and 50 mg/L (calculated as Cd). Each treatment was replicated three times. The seedlings were aerated 3 h everyday. Root tip segments (3 cm) were used to determine the content of Cd 0.1g dried root samples were ground and the powder was digested with a mixture of HNO3＋HCl＋HClO4 3∶2∶1.5). Samples were evaporated to dry on a plank heated by electricity at 300℃. The elements were extracted with 10% HCl. The samples were put in inductively coupled plasma to determine content of Cd. The content of superoxide anions was assayed according to the method of colorimetry; The content of soluble protein and the activity of GR and APX was determined with UV spectrophotometer; The activity of SOD was determined according to the method of nitroblue tetrazolium; The activity of CAT was determined according to visible spectrophotometry; The content of MDA was determined according to the method of thiobarbituric acid reaction; The activity of POD was determined according to colorimetry; The level of phytohormones was assayed according to the enzyme-linked immunosorbent assay. The results showed that the content of superoxide anions increased with the concentration of Cd. The content of soluble protein increased at 5mg/L of Cd, but decreased at higher Cd concentration. Activities of SOD, CAT and APX increased at 5mg/L Cd, but decreased at higher Cd concentration. Activities of POD and GR increased at the 5-25mg/L range of Cd, then decreased at 50 mg/L of Cd, but was still higher than the control. The content of MDA increased with concentration of Cd. Activity of IAA oxidase increased at 5mg/L of Cd, but decreased with the increase of Cd concentration. The content of IAA and GA at 5mg/L of Cd, but decreased at higher Cd concentrations. With Cd concentration increasing, the content of ABA gradually increased, while the content of ZR sharply decreased. This study will help us to further understand Cd toxicity to tobacco roots.