Objectives: The objectives of this study were to examine the ability of biofilm production in Acinetobacter baumannii clinical isolates under in vitro conditions, to investigate their antimicrobial resistance by the dilution method, and to demonstrate a correlation between antibiotic susceptibility of A. baumannii isolates and their biofilm production ability. Material and methods: This study used 47 clinical isolates of A. baumannii collected from 2007-2019 and stored at the Public Health Institute of Osijek-Baranja County. Tested bacteria was inoculated into 3 ml of Luria-Bertani broth for 24 hours in a thermostat at 37 ˚C, after which 20 µl was transplanted to new LB broths, and 5x105 density suspension was also prepared by this procedure. The suspensions were mounted on flat bottom microtiter plates, and the biofilm reading was spectrophotometrically on a reader at 492 nm. Obtained results were classified into four categories. The final step was to determine the antimicrobial resistance by the dilution method of the selected antibiotics. Results: The results show that the tested Acinetobacter baumannii isolates successfully and statistically significant produce biofilm and that the susceptibility of the tested isolates to antibiotics is also statistically significant. Furthermore, the results indicate a correlation between antibiotic susceptibility and biofilm production, so isolates with lower biofilm production show higher antibiotic susceptibility, while those with higher production are more resistant. Conclusion: This and related studies that provide insight into the correlation of biofilm production and increased antimicrobial resistance under in vitro conditions lead to the invention and development of targeted antimicrobial therapy for preventing the onset and suppression of biofilm already formed in vivo.