Background:             The crystalline biofilms formed by Proteus mirabilis can seriously complicate the care of patients undergoing bladder catheterization, the prevention of crystalline biofilms is important to avoid urinary catheter complications. The surfactant of Lactobacillus acidophilus can be interacting with attachment of many microorganisms. Aims of the study: 1-      To detect the biofilm formation ability of Proteus mirabilis isolates in urinary catheter. 2-      To detect the growth and biofilm formation ability of Proteus mirabilis isolates on 96-wells microtiter plates. 3-      To study the role of Lactobacillus acidophilus surfactant in biofilm formed by Proteus mirabilis isolates. Materials and methods: Since Jan/2011 to Jan/2012 a 48 isolates of Proteus mirabilis were isolated from the encrusted catheter of a patient undergoing indwelling catheterization in Al-Ramadi General Hospital while Lactobacillus acidophilus isolate was obtained from urogenital tracts of healthy woman by vaginal swab and surfactant was extracted from it. The biofilm formation on catheters, quantitative assays of biofilm formation and biofilm inhibition assay by surfactant were studied. Results: Fourty five 45 (93.75%) P. mirabilis isolates produced a biofilm in urinary catheter while 3 (6.25%) isolates were not produce biofilm while 48 (100%) isolates forms good biofilms results on 96-wells microtiter plate, in brain heart infusion broth with 0.2% glucose, and at 37°C. The growth of P. mirabilis isolates in 96-well microtiter plates were determine at OD630, the optimum growth of P. mirabilis isolates were recorded after 48 hours of incubation (OD630= 0.65). Biofilm kinetics of P. mirabilis isolates refers to that attached cells increased with time and the maximum biofilm formation ratio occurs at 48 hours of incubation (OD550= 0.70). Surfactant show a good ability to inhibit biofilm formation, the increasing amounts of surfactant led to a decrease in the amount of biofilm formed by P. mirabilis isolates and that 6.0 µg/ml of surfactant was more than sufficient to completely abolish biofilm formation.