The 9-bp deletion in the COIl/tRNALys intergenic region (region V) of human mitochondrial DNA was screened in 1521 Chinese from 16 ethnic groups and 9 Han geographic groups. The highest frequency was found in populations of Miao (32.4%) and Bouyei (30.8%) from Guizhou Province, whereas no deletion was found in Kazak population in Xinjiang. In the populations of Wa and Lahu from Yunnan Province, Uygur and Mongolian from Xinjiang,the deletion frequency was relatively low ( ≤ 4 % ), while in the remaining 18 groups, the frequency was moderate (6 % ～ 24% ). Except those Hans in Xinjiang, Guizhou and that reported in Taiwan, the deletion frequency in the Han geo graphic groups did not show a substantial difference. However, the deletion frequency in some ethnic groups from the same geographic region or with similar ethnohistory did not show similarity. A general decrease tendency in the deletion frequency was found from south to north and from coastal to inland. The frequency of the 9-bp deletion was approximate ly 17.20% in all Chinese we studied and reported elsewhere. Additionally, 4 individuals were found to carry the tripli cation of 9-bp segment in region V; one individual had X. II type of 9-bp deletion; and no other length polymorphisms were detected in this region in 27 randomly selected individuals with or without the deletion.