Abstract: Toxicity effects of terbium on horseradish growth were studied.The results show that the chlorophyll can be induced at the low concentration of Tb³⁺, and destroyed as the increasing of Tb³⁺ concentration. Tb³⁺ can induce rise of the activity of horseradish peroxidase(HRP) at lower concentration,and decrease at high concentration.However,the permeability and MDA content appear first decrease and then increase trend.When the concentration is 3mg/kg,all the indexes reach the maximum or minimum;for horseradish,the threshold limit is about 10mg/kg.By the analysis of significance of the index difference,HRP is most sensitive to Tb³⁺，indicating that the peroxidase may be regarded as the good index of the heavy rare earth toxicity.