Abstract: Research is focused on the composition and quantitative variation of heterotrophic bacteria attached on the surface of cuprous oxide antifouling paint. The results show that the heterotrophic bacteria are composed of Aeromonas, Photobacterium, Pseudomonas and Vibrio, etc. The bacteria are identified to genus level as motile, Gram negative rod with flagellum. Aeromonas is the predominant group in immersing primary stage, however, with immersing time going on, the predominant group frequently changed. Bacterial quantitation increases swiftly in early period and reaches its maximum number after three or four days, then keeps a constant state of balance. All this indicated that a mature slime biofilm formed gradually.