Abstract: The acute toxicity of Terbium (Tb) to zebrafish (Danio rerio) was investigated by a semi-static acute exposure test. Based on the acute toxicity test, the concentration groups of low (2.0 mg/L), medium (20.0 mg/L), and high (40.0 mg/L) of Tb were set up to determine the toxicological effects of Tb on zebrafish by analyzing catalase (CAT) activity and malondialdehyde (MDA) content in three tissues (head, muscle and viscera) of zebrafish. The results showed that a high concentration of Tb was more toxic to zebrafish. The 48 h and 96 h median lethal concentrations (LC₅₀) of Tb to zebrafish were 81.39 mg/L and 79.03 mg/L, respectively. The safe concentration (C_S) was 7.90 mg/L. Terbium (Ⅲ) ion (Tb³⁺) had different effects on CAT activity in various parts of zebrafish. CAT activity decreased gradually with the increase of Tb concentration. With increased exposure time in muscle and viscera, CAT activity was initially induced and then significantly inhibited, while it did not recover in viscera during the purification period in the 40mg/L group. Under Tb stress, the MDA content in viscera of zebrafish showed repeated induction-inhibition changes, while MDA content in muscle exhibited an obvious induction effect during stress, peaking 57.13% on the 14th day after exposure. The visceral MDA content of zebrafish treated with 40.0 mg/L concentration was still significantly induced at the purification phase, with the highest induction rate of 28.99%. The study revealed the acute toxicity and oxidative stress toxicity of Tb to zebrafish and provided a reference for preventing and reducing the toxicity of rare earth ions to aquatic organisms.