Objectives: The aim of the study was to investigate the direct and indirect – mediated by job burnout – effects of job demands on mental and physical health problems. The Job Demands–Resources model was the theoretical framework of the study. Three job demands were taken into account – interpersonal conflicts at work, organizational constraints and workload. Indicators of mental and physical health problems included depression and physical symptoms, respectively. Material and Methods: Three hundred and sixteen Polish teachers from 8 schools participated in the study. The hypotheses were tested with the use of tools measuring job demands (Interpersonal Conflicts at Work, Organizational Constraints, Quantitative Workload), job burnout (the Oldenburg Burnout Inventory), depression (the Beck Hopelessness Scale), and physical symptoms (the Physical Symptoms Inventory). The regression analysis with bootstrapping, using the PROCESS macros of Hayes was applied. Results: The results support the hypotheses partially. The indirect effect and to some extent the direct effect of job demands turned out to be statistically important. The negative impact of 3 job demands on mental (hypothesis 1 – H1) and physical (hypothesis 2 – H2) health were mediated by the increasing job burnout. Only organizational constraints were directly associated with mental (and not physical) health. Conclusions: The results partially support the notion of the Job Demands-Resources model and provide further insight into processes leading to the low well-being of teachers in the workplace.