With culture-independent approach, microbial total DNA was directly extracted from Pachychalina sp. Using the total microbial DNA as template, archaeal 16S rDNAs were amplified by PCR with universal primers. Amplified products were cloned into T-vector and secondarily amplified by PCR. Then the secondarily amplified products were purified to be further characterized by termed ARDRA (amplified rDNA restriction analysis). According to the enzyme restriction mapping, the apparent difference among them were disclosed. Furthermore eight archaeal cloned partial sequences were acquired and built up a phylogenetic tree. In the phylogenetic tree, the eight archaea belonged to Methanogenium organophilum and Methanoplanus petrolearius, but the 16S rDNAs similarities among them and those archaea registered in RDP Database didn't excess to 90%. It means that they maybe represent some novel archaeal groups.