Abstract: Effect of 2, 4-brassinosteroid on the growth of barley (Hordeum vulgare) seedlings under Cd-stress were studied by an indoor culture experiment. In comparison with control, the treatment of Cd at 20 mg·L^-1 inhibited the seedling growth and damaged the leaf physiology manifesting in the decreased root length and plant height, reduced contents on biomass, chlorophyll, soluble sugars and soluble protein, declined activities of POD and CAT, increased relative electrical conductivity, heightened contents of MDA, O₂^- and proline, and elevated activity of SOD. After spraying 2, 4-brassinosteroid at 0.2 mg·L^-1, the Cd-stressed seedlings significantly increased on the root length, plant height, biomass and chlorophyll. The treatment promoted the photosynthesis and seedling growth, reduced the leaf relative conductivity, MDA and O₂^-, and facilitated an osmotic adjustment with the substances (e.g., soluble sugars, proline and soluble protein), and enhanced the antioxidant enzymatic activities on SOD, POD and CAT. It appeared that the plant hormone could alleviate the ill-effects of Cd-stress on and enrich the adaptability in the battle against the adversity for the barley seedlings.