Abstract The mixed fouling process of Pseudomonas fluorescens and CaCO 3 on different solid surfaces in a simulated cooling water system has been investigated. The mixed fouling behavior on different solid surfaces under the condition of different CaCO 3 saturation levels and bulk velocities has been examined, and the growth curves of mixed fouling have been obtained. The results show that the mixed fouling behavior on various material surfaces depends mainly on the affinity of bacteria to a material. The mixed fouling mass developed on polymer materials is much more than that on metal surfaces. With the increase of saturation level of CaCO 3, however, this difference becomes minimal. The results also indicate that the mixed fouling mass decreases with the increase of CaCO 3 saturation degree and velocity. The induction period of mixed fouling declines with the rising of velocity. Moreover, the induction period of mixed fouling is longer than that of pure biofouling when the saturation level of CaCO 3 is less than 1 and greater than 0. The induction period decreases with CaCO 3 saturation degree when the level is more than or equal to 1. In addition, the sequence of adhesion and deposit of the bacteria and CaCO 3 on a glass surface was measured with micro-video technology. The results show that CaCO 3 first deposits on the solid surface, while the bacteria need longer time to adhere on the surface.