Diabetes mellitus in Long-Evans Tokushima Lean (LETL) rats closely resembles type 1 diabetes in human beings, e.g., no gender differences in the incidence of diabetes and no T lymphopenia. Although the LETL rats have been established as an inbred strain, the incidence of diabetes is only approximately 20%. In the present study, we established two substrains, one a diabetes-prone (KDP) and the other a non-diabetic (KND) from the original inbred LETL rats. The features of KDP rats are a high incidence of diabetes (over all approximately 70%) without lymphopenia and 100% development of mild to severe insulitis at 120-220 days of age. In contrast, the KND substrain is characterized by the complete absence of diabetes incidence. Among 165 SSLP marker loci throughout all rat chromosomes, no loci showed variation among KDP and KND substrains and their parental LETL rats. In this regard, the genetic background of these two substrains, KDP and KND, appears to be uniform except for the major gene(s) that is responsible for the diabetes. In this context, these two substrains of LETL rats should serve as useful tools for research on the pathogenesis and for the genetic analysis of type 1 diabetes. In this report, we have not only established, but also characterized these two substrains, and provided their fundamental data.