This study aimed to determine the mediating effect of organizational diagnosis on the relationship between motivation and job satisfaction of librarians in Region XI. The descriptive correlation technique utilized a non-experimental quantitative research design employing the descriptive correlational method in this study. The research used adapted questionnaires modified to suit the studys objectives. A total of 132 librarians as respondents through stratified-random sampling surveyed. Mean, Pearson-r, and Path Analysis are statistical tools employed in analyzing and interpreting the data. The researcher personally supervised and administered the questionnaire to the respondents through google forms survey to ensure accuracy and prevent the occurrence of ambiguity. Results showed that librarians posted a very high level of motivation, also a very high level of job satisfaction, and a very high level of organizational diagnosis resulting from partial mediation. Findings also revealed a significant relationship between motivation and job satisfaction, motivation and organizational diagnosis, and organizational diagnosis and job satisfaction. This research observed a partial mediation of the effect of organizational diagnosis on the relationship between motivation and job satisfaction; thus, organizational diagnosis is one of the reasons why motivation can influence job satisfaction.