Aim: This study aimed to investigate the prevalence of gram negative and gram positive bacteria in addition to the investigation of antibiotic resistance rates in 2021 at a military hospital in Riyadh Region. Materials and Methods: This observational study included the retrospective review of bacterial isolates from 1 st of January 2021 to 30 th of June 2021. Results: Most of the infections were caused by gram negative bacteria (64.52%). The most common gram negative bacteria were Escherichia coli (43.63%) followed by Pseudomonas aeruginosa (20.52%). The most common gram positive bacteria were Staphylococcus aureus isolates (71.74%). The study also showed that Acinetobacter baumannii was a pandrug-resistant bacterium and Enterobacter cloacae, Proteus mirabilis, Morganella morganii, and Enterococcus faecalis bacteria were multidrug resistant. Conclusion: There was a high resistance for some bacteria to numerous antibiotics. Antibiotic susceptibility testing is an essential guide for physicians to help them in the selection of the suitable antibiotic for bacterial infections.