The present study was carried out on 10 mongrel healthy dogs. Complete unilateral ureteral obstruction was performed in all animals under the effect of general anaesthesia. The studied animals were classified into 5 groups each of two dogs. They were euthanized 15 days, one month, two months, 4 months and 9 months following operation. Before euthanasia excretory urography was performed to evalute renal function. Gross findings of both
kidneys for each group were recorded and samples were taken for histopathological examination Excretory urography indicated that, the kidney of the ligated side lost its function at 15 days following ligation, then its function returned partially till 4 months following ligation then lost its function completely. Hydronephrosis was the end result of complete unilateral ureteral obstruction which occured within the first month following operation then the kidney underwent atrophy. Pathological changes were noted in the glomeruli at 15 days following obstruction. Complete fibrosis of most glomeruli and complete destruction of most collecting tubules occured at 4 months following obstruction Contralateral kidney showed compansatory hyperatrophy manifested by increase in the number of functional glomeruli without any significant increase in the gross finding of this kidney