Abstract: Twenty strains of bacteria from the cyanide-containing wastewater were isolated. The plasmid DNA of the 20 strains were not only isolated but also digested by restriction endonuclease and agarose gel electrophoresis. Eleven strains were found to contain plasmids. The experiment of cyanide degrading was then made on the bacteria containing plasmids and those not containing plasmids. The experiment explained that appearance of plasmids is important to cyanide-degrading bacteria. At the same time, the authors analyzed molecule size of plasmid, but did not find the correlation between the molecule size and the ability of cyanide degrading. In the gram coloration experiment, it was found that 20 strains were all gram negative of stick bacteria.