Abstract: The survival and stability of Aeromonas hydrophila(Ah)strain 4332GFP marked with green fluorescent protein plasmid(pGFP)in the warm water was tested. The results showed that Ah4332GFP survived 47 d and the number of green fluorescent cells(GFCs)had two peaks in the autoclaved pond water. In the natural pond water, Ah4332GFP survived 18 d, but the number of GFCs declined during the experimental period. It suggested that Ah4332GFP and the natural bacteria in the pond water interacted and affected the stability of marked bacteria. In the medium M9, Ah4332GFP strain could culture to 40 and 70 generations and the rates of stability of pGFP were 47.3% and 20.5%, respectively. It concluded that pGFP had relative stability and Ah4332GFP could be applied to bacterial ecology survey.