Abstract: To provide references for screening Chinese herbal medicine against fish parasites by Tetrahymena thermophila, we studied the effects of Chinese herbal monomers (CHM) such as artemisinin, emodin, aloe-emodin and berberine on the growth and apoptosis of T. thermophila by Hoechst 33258 fluorescence staining, living cell counting, CCK-8 (Cell Counting Kit-8) cell viability test and antioxidase activity assay. The results show that with Hoechst 33258 fluorescence staining, T. thermophila cells in the CHM groups appeared significantly stronger fluorescence than those of the control groups at high concentration (20−200 mg·L⁻¹), which indicates that the four kinds of CHMs can cause apoptosis of T. thermophila cells. The 50% inhibitory concentration (IC₅₀) and 95% confidence intenal (95% CI) of the four monomers to T. thermophila cells determined by living cell counting method was 21.23 (16.71−28.23) mg·L⁻¹, 3.77 (1.91−5.54) mg·L⁻¹, 1.70 (0.18−3.82) mg·L⁻¹ and 44.56 (29.82−98.66) mg·L⁻¹, respectively; and 20.03 (13.02−28.45) mg·L⁻¹, 6.07 (4.39−7.65) mg·L⁻¹, 3.67 (2.61−4.72) mg·L⁻¹ and 107.39 (66.78−267.17) mg·L⁻¹ determined by CCK-8 cell viability test, respectively, consistent with the results by living cell counting method. When the monomer concentration was 1.25−50.0 mg·L⁻¹, with the increase of drug concentration, the activities of catalase (CAT) increased, malondialdehyde (MDA) decreased, and superoxide dismutase (SOD) increased first and then decreased. In conclusion, the four kinds of CHMs affect the proliferation and the growth and apoptosis of T. thermophila were dose-dependent. The occurrence of apoptosis may be related to the change of cellular oxidative stress.