Mitochondrial DNA isolated from 4 chinese vipers(Agkistrodon blomhoffii brevicaudus) was digested with 10 restriction endonucleases. One out of four individuals was heteroplasmic in mtDNA size and restriction sites. Rest of them were, however, homoplasmic. Heteroplasmic individual showed two types, about 17.5 and 22.0 Kb of genome size, which were obtained in Hind III and Pst I enzyme digests distinctively. In other enzyme digests, both mtDNA size and restriction site differences were observed. Heteroplasmy was usually caused by base substitution or addition/deletion of small fragments in other animals. Likewise, the larger mtDNA in heteroplasmic one could be attributed to and addition of 4.5Kb fragment.