Abstract: An outbreak of poxvirus infection was occurred in a Wistar rat colony,with a morbidity of 33.3% (10/30). The clinical signs and the pathohistological findings of the tail skin, liver and spleen lesions were identical with those of mouse pox. The DNA of the virus was found in the epithelial cytoplasm by using Feulgen stain. Suspension of the homogenized liver and spleen tissues were inoculated onto chorioallantoic membranes of 12 - day chick embryos. Pocks were appeared on the membranes at the fourth passage. Electron microscopic examination revealed the presence of poxvirus in both the chorioallantoic membranes and the suspension of the homogenized tissues.