Forty Y-STR loci were analyzed in 1128 males from the following six Chinese ethnic populations: Han (n=300), Hui (n=244), Korean (n=100), Mongolian (n=100), Uighur (n=284) and Tibetan (n=100), utilizing two new generation multiplex Y-STR systems, AGCU Y24 STR and GFS Y24 STR genotyping kits, which allow for the genotyping of 24 loci from a single amplification reaction in each system. The lowest estimates of genetic diversity (below 0.5) correspond to markers DYS391 (0.441658) and DYS437 (0.496977), and the greatest diversity corresponds to markers DYS385a/b (0.969919) and DYS527a/b (0.94676). A considerable number of duplicate and off-ladder alleles were also revealed. Additionally, there were 1111 different haplotypes identified from the total 1128 samples, of which 1095 were unique. Notably, no shared haplotypes between populations were observed. The estimated overall haplotype diversity (HD) was 0.999085, and its discrimination capacity (DC) was 0.970745. An MDS plot based on the genetic distances between populations showed the genetic similarity of the southern Han population to the Northern populations of Hui, Korean, Mongolian and Uighur and a clear genetic departure of the Tibetan population from other populations. For the Y STR markers, population substructure correction was considered when calculating the rarity of the Y STR profile. However, because the haplotype based Fst values are extremely small within the present data (0.000153 with 40 Y-STRs), no substructure correction is required to estimate the rarity of a haplotype comprising 40 markers. In summary, the results of our study indicate that the 40 Y-STRs have a high level of polymorphism in Chinese ethnic groups and could therefore be a powerful tool for forensic applications and population genetic studies.