The $Km^{r}$ gene and plasmid of natural isolate and genetically modified microorganisms (GMM) rearranged by conjugation in water environments were comparatively analyzed by agarose gel electrophoresis and Southern analysis. The transfer rates of the $Km^{r}$ gene from GMM strains were generally 100 times higher than thosc of natural iso]ate(DKI) under laboratory cnvironments, but their transfer rate was not much different in Moosimcheon River water. The conjugants obtained in LB(Luria-Bertani broth) and FW(filtered river water) water under laboratory conditions showed same number of the plasmids. but the sizes of the plasmids were changed. The $Km^{r}$ gene in the conjugants was found in the same position as the pDKJO] $Km^{r}$ plasmid. In case of the GMM strains as donor. the large plasmids of 180 kb appeared in conjugants obtained in LB and FW water. Especially, the $Km^{r}$ gene in the donor of DKC600 was found to be inserted into chromosome of the conjugant obtained in FW water. However. in the conjugants obtained from DKl and DKB 701 in Moosimcheon River water, the plasmids were rearranged by 4 and 8. respectively, and all of them showed hybridization by the $Km^{r}$ probe. But the small plasmids of the recipient disappeared in the conjugant from DKC600 as donor, and the rearranged plasm ids and chromosome in the conjugants were observed to be hybridized with the $Km^{r}$ probe. Therefore, rearrangement of $Km^{r}$ gene and plasmids by conjugation was found to be afTected diversely by cellular characteristics as well as by environmental factors.