This study was based on 3 necropsies of patients affected with Balantidium coli dysentery from two pig farms. Grossly, the lesions involved the large intestine from cecum to rectum. Many variable-sized ulcers were diffusely scattered on the mucosa of the cecum and the colon which were covered with a necrotic, grayish white, slate black, or black membrane. The mucosa affected reddened and swollen. Microscopically, numerous balantidia penetrated in the mucosa of the colon and there they induced necrosis and desquamation of the epithelial cells, where inflammatory cells such as macrophages, neutrophils, eosinophils, lymphocytes and plasma cells were infiltrated.