Genomic DNA samples extracted from blood stains from 484 lineage members from North Chinese Han population were genotyped with TYPERX19 kit. In a total of 5 652 allele transmissions, 8 mutations were detected from 6 different markers including DXS6810, DXS8378, DXS6797, DXS7423, DXS7424, DXS8377 through the 484 lineage members, the mutation rate of DXS6810 and DXS8377 was 0.006 4, the mutation rate of DXS8378, DXS6797, DXS7423 and DXS7424 was 0.003 2. No mutation was found in the other 12 markers. The average mutation rate across all 18 X-STR markers was 0.001 4. All mutations were with single step. There were no significant differences between mutation rates of different X-STR loci (P＞0.05). The losses and gains were balanced at all loci. Mutation rates were correlated with the lengths of the alleles. Alleles with higher number of repeats were more likely to mutate. The origins of the mutation are mostly from the fathers.Biography: YU Zhengliang.