Abstract： Objective We analyzed SNPss and the deviation from the standard sequence in Cyt-b of mitochondrial DNA in 96 patients with type 2 diabetes and 96 centenarians.Methods Total DNA was extracted from the blood of 96 type 2 diabetes patients and 96 centenarians.Mitochondrial Cyt-b genes were amplified by use of oligonucleotide primers.Sequences were analyzed by direct sequencing.Mitochondrial SNPss were identified by comparison with the revised Cambridge reference sequence.Results The number of the carried SNPss with each individual in diabetes group was significantly higher than that in centenarians group when the shared common SNPss were excluded from summation(P=0.01).The number of carried SNPss of each individual in type 2 diabetes group was significantly higher than that in centenarians group when the shared common amino acid replacements were excluded from summation(P=0.02).The deviation from the standard sequence in diabetes group was significantly higher than that in centenarians group(P=0.03).Conclusions The most mitochondrial SNPss within a species are mildly deleterious in type 2 diabetes.The deviation from the standard sequence in Cyt-b is higher in type 2 diabetes than in centenarians