Nihon rat is a novel rat model that was recently discovered from a colony of Sprague-Dawley strain to develop renal cancers in a hereditary manner. It has already been reported in this model that renal tubular adenomas were developed at 16 weeks of age. A peculiar feature is seen in the cell type consisting of these lesions where the clear cells predominate as found in human renal cancers. Southern blot, northern blot and SSCP analyses on TSC1, TSC2, VHL and c-Met, all of which are incriminated in hereditary renal cancers, revealed no mutation present in Nihon rats. When the kidneys were microscopically carefully examined from Week 0 age to characterize the onset of the renal lesions of Nihon rats, atypical renal tubules considered to be precancerous changes were present as early as 3 weeks of age, and the adenomas were found at 8 weeks of age. Transplacental administration of N-Ethyl-N-Nitrosourea to neonates resulted in accelerating the onset and increasing the number of tumors per rat. Thus, Nihon rat in which renal tumors as well as precancerous lesions are developed from very early age will serve as a useful rat model for research on renal cancers.