Background: Lower respiratory tract infections, specifically pneumonia, are a leading cause of morbidity in children and are predominantly caused by viral and bacterial pathogens. Researchers worldwide have reported that the etiology of pneumonia varies significantly with age, noting an increasing incidence of Mycoplasma pneumoniae pneumonia (MPP) among children over five years of age. In the context of Mongolia, investigating the incidence, clinical presentation, and laboratory and diagnostic imaging characteristics of MPP is essential. Understanding these specific features will facilitate early detection and optimal treatment, preventing potential complications. Furthermore, this research aims to reduce the unnecessary use of antibiotics by ensuring accurate diagnosis, which serves as the primary rationale for this study. Aim: To investigate the clinical characteristics of Mycoplasma pneumoniae pneumonia (MPP) in relation to laboratory findings and diagnostic imaging changes. Materials and Methods: A retrospective study was conducted at the Pediatric Ward of the National Center for Maternal and Child Health-2 (NCMCH-2). Data were collected using quantitative methods. Information from patient questionnaires, physical examinations, and laboratory test results were coded for analysis. Statistical analysis was performed using Microsoft Excel and SPSS version 30.0. Results: Analysis of the pathogens causing pneumonia across different age groups revealed that mixed viral and bacterial co-infections predominated in younger children. Conversely, bacterial infections became the primary cause as age increased, indicating a significant age-dependent variation in pathogen distribution (p=0.00054). Based on PCR testing, Mycoplasma pneumoniae (MP) was the most frequently detected pathogen, identified in 51.8% (55) of cases. The mean age of children positive for MP was 9.4 ± 4.4 years. Among these cases, only 25% (14) presented as MP monoinfection, while 75% (51) involved co-infections with other bacterial and viral pathogens. Conclusions 1. Mycoplasma pneumoniae was identified as the most prevalent bacterial pathogen (51.8%) among children hospitalized with pneumonia, indicating a high incidence of pneumonia caused by this bacterium during the late months of 2024. 2. Mycoplasma pneumoniae infection primarily affects school-aged children (mean age 9.2 years). Despite presenting with abnormal breath sounds upon auscultation requiring hospitalization, children positive for MP exhibited normal oxygen saturation and normal inflammatory markers in the blood compared to the MP-negative group. This highlight the classic «atypical» nature of the pathogen. Furthermore, clinical manifestations vary across age groups; specifically, upper respiratory symptoms such as rhinorrhea predominate in younger children (likely due to viral co-infection), whereas these symptoms significantly decrease in older children, in whom lower respiratory tract symptoms become dominant.