Abstract: On promoting next-generation breeding of forest trees, it is necessary to consider about selection of candidate trees and crossing parents taking care of blood relationship, in order to maintain genetic diversity and minimize increases in the inbreeding coefficient due to a reduction in the size of the breeding population. We therefore evaluated genetic diversity of first- and second-generation plus tree populations of Hinoki（Chamaecyparis obtusa）in the Kansai breeding region using nuclear SSR (simple sequence repeat)markers, and estimated the genetic contributions of first-generation parents to the second-generation by performing parentage analysis. The mean effective number of alleles and the gene diversity of the second-generation were not significantly lower than those of first-generation in the Japan Sea and Kinki-Seto Inland Sea areas, but they were in the Shikoku area. Parentage analysis revealed that 112 out of 264 second-generation clones (42.4%) could be assigned to a single first-generation paternal parent. Compared to maternal parents, genetic contribution frequencies were skewed towards paternal parents, and a smaller number of first-generation paternal parents contributed to the second-generation at high frequencies. The present study is the first to evaluate the genetic diversity of the next-generation breeding population in Japanese major forestry species. The insights obtained provide fundamental information for ongoing diffusion and breeding programs.