Background: Nurses play a central role in pain assessment, treatment monitoring, and clinical decision-making. Their competence in pain management and medication safety directly affects the quality and safety of care. Inadequate knowledge increases the risk of pain underassessment, inappropriate medication use, and delayed detection of adverse effects. However, comparative evidence on nursing competencies between the Mongolian–Japanese Hospital (MJH) and the International Mongolian Hospital of Inner Mongolia (IMHOIM) remains limited. Aim: To assess and compare nurses’ levels of pain management knowledge and to examine factors associated with knowledge differences. Materials and Methods: An analytical cross-sectional study was conducted between December 2024 and March 2025, involving 212 nurses from MJH and IMHOIM. Data were collected using the internationally validated Knowledge and Attitudes Survey Regarding Pain (KASRP; 39 items, Cronbach’s α=0.851). Statistical analyses were performed using IBM SPSS Statistics version 26, including descriptive statistics, independent samples t-test, ANOVA, Mann–Whitney U test, Pearson correlation, and stepwise linear regression. Statistical significance was set at p<0.05. Result: Participants differed significantly by age, educational level, professional rank, and years of experience between the two hospitals. The overall mean knowledge score varied significantly by institution, with IMHOIM nurses scoring higher than MJH nurses (26.69±7.55, 19.88±5.21; p<0.001). Domain-specific analysis indicated that IMHOIM nurses outperformed in foundational and pharmacological knowledge, whereas MJH nurses showed superior performance in clinical decision-making and case-based items (p<0.001). Years of experience demonstrated a moderate positive correlation with knowledge scores (r=0.434, p<0.001); however, educational level and professional rank emerged as the strongest independent predictors in regression analysis. Conclusion Nurses’ pain management knowledge differs by institution, reflecting variations in theoretical and clinical competence. Work experience alone is insufficient; higher education, professional rank, and continuous case-based clinical training are critical. Accordingly, pain management education should emphasize evidence-based, clinically oriented programs to strengthen clinical decision-making skills.