The microbiological influenced corrosion (MIC) behavior of a marine pipeline Cu-Ni alloy in the sterile seawater and sulfate-reducing bacteria (SRB) solution was investigated. Results show that severe pitting corrosion appeared on the specimens in the SRB solution. The corrosion potential of specimen in the SRB solution was much lower than that in the sterile seawater and the polarization resistance of specimen in the SRB solution decreased quickly after a period immersion and became much lower than that in the sterile seawater. Besides, the results of EDS and XRD show that the content of element Ni and Fe of the Cu-Ni alloy decreased greatly and the high content of element S appeared after 30 days immersion in the SRB solution. It was concluded that the SRB accelerated the corrosion process of the Cu-Ni alloy greatly. The MIC mechanism of the alloy in marine environment is discussed.