Abstract: Objective To investigate the ultrastuctural changes of the extraintestinal organs of newborn mice with human retrovirus (RV) infection to probe into the mechanism and clinical diagnose and therapy of extraintestinal RV infection. Methods Human RV was inoculated into the abdominal cavity of the newborn mice, and the ultrastructural changes of the heart, lung, livers, and kidneys of the infected and control mice were observed by transmission electron microscope. Results The mice with intraabdominal RV injection showed pathological changes of the cells in the small intestinal villus, liver, and kidneys. Shortened small intestinal villus, nuclear membrane disorganization, massive vacuolization, mitochondrial swelling and rough endoplasmic reticulum dilation were observed in the cells of the small intestinal. In the liver of the mice, marked mitochondrial swelling and agglutination, cell nucleus pyknosis or collapse, presence of numerous lipid droplets and vacuoles were seen in the liver cells, with lymphocyte and plasmacyte infiltration. Obvious dilatation and shedding of the microvillus were seen in cholangioles. The mitochondria of the proximal convoluted renal tubule showed mild swelling, but the cells in the heart and lung did not display obvious changes. Conclusion The small intestinal villi were highly susceptible to RV infection, and systemic spread of human RV may cause damage of various extraintestinal organs especially the liver, which can also be susceptible to RV.