Background: Pulmonary infections remain a major cause of global morbidity and mortality, particularly in low- and middle-income countries. The rapid emergence of antimicrobial resistance, including multidrug-resistant, extensively drug-resistant, and pandrug-resistant organisms, has significantly limited therapeutic options and increased healthcare burden. This study aimed to investigate the bacterial profile and antimicrobial resistance patterns among patients with suspected pulmonary infections at a tertiary referral hospital in Mongolia.Methods: A retrospective descriptive study was conducted at Mongolia–Japan Hospital in Ulaanbaatar, from January 1, 2023, to December 31, 2024. Data were extracted from the electronic medical record system. Patients who underwent microbiological examination of lower respiratory tract specimens (sputum, bronchial washing, bronchoalveolar lavage) were included. Bacterial identification and antimicrobial susceptibility testing were performed using the VITEK-2 system in accordance with CLSI M100 guidelines. Resistance phenotypes were classified based on CDC and ECDC criteria. Statistical analysis was conducted using SPSS version 26, with chi-square testing applied for group comparisons. A p-value < 0.05 was considered statistically significant.Results: A total of 354 patients were included, with a balanced gender distribution and predominance of older adults. Bacterial pathogens were identified in 78.0% of cases. The most frequently isolated organisms were Klebsiella pneumoniae (36.2%), Acinetobacter baumannii (17.0%), methicillin-resistant Staphylococcus aureus (10.9%), and Pseudomonas aeruginosa (6.2%). Gram-negative bacteria predominated and demonstrated high resistance rates. Among K. pneumoniae isolates, 23% were MDR, 8% XDR, and 4% PDR. A. baumannii exhibited 14.9% MDR, 6.4% XDR, and 31.9% PDR. MDR was observed in 73.3% of MRSA isolates. Resistance rates were significantly higher in the Internal Medicine Department (MDR 39.7%) and ICU (XDR 37.1%) compared to the outpatient department (p < 0.001). MDR was significantly associated with cardiovascular disease, chronic kidney disease, rheumatoid arthritis, diabetes mellitus, and hematological disorders (p < 0.05). Mortality was significantly higher among patients with bacterial growth compared to culture-negative patients (18.8% vs. 2.9%, p < 0.05), with pneumonia being the leading cause of death.Conclusions: Gram-negative pathogens, particularly K. pneumoniae and A. baumannii, predominate in pulmonary infections and demonstrate alarming levels of MDR, XDR, and PDR phenotypes. High resistance rates in ICU and internal medicine settings highlight the urgent need for strengthened infection prevention and control measures and robust antimicrobial stewardship programs. Continuous surveillance, regular antibiogram updates, and multicenter prospective studies incorporating molecular resistance detection are essential to optimize empirical therapy and mitigate the growing burden of AMR in Mongolia.