Potassium permanganate, formalin and NaOH were selected to determine their median lethal concentration(LC50) based on the absolute lethal concentration(LC100) of these disinfectants to kill trophozoites of sheep balantidium coli. The results showed that LC50 doses of potassium permanganate, formalin and NaOH to kill trophozoites of sheep balantidium coli were 8.531×10~(-4), 4.213×10~(-4) and 10.50×10~(-4) within 2 hours and 6.502×10~(-5), 8.267×10~(-5) and 10.31×10~(-5) within 12 hours, respectively. Theref...