Biofilms are surface-attached microbial communities with phenotypic and biochemical properties distinct from free swimming planktonic cells. The capability of the gram-negative predatory bacterium Bdellovibrio bacteriovorus to control and reduce an existing Serratia marcescens biofilm was evaluated by colony biofilm assay. A reduction in biofilm biomass was observed as early as 2 h after exposure to the predator, and as much as 75% reduction after 6hrs of exposure. The ability of B. bacteriovorus to reduce an existing biofilm was confirmed by reduction in CFUs after exposure of predator.