The main purpose of this study was to examine the burnout process using longitudinal data.Questionnaires were administered to 138 human service professionals (nurses and caregivers) twice at intervals of a year. The models of causal relations among three dimensions of burnout were examined by structural equation modelling (SEM). As a result of this analysis, the Leiter&Maslach (1988) model, which predicts that emotional exhaustion influences depersonalization, while depersonalization reduces personal accomplishment, was most consistent with the data. Furthermore, the longitudinal model fits the data better than the synchronous one, suggesting that burnout should be considered as a developmental process. Implications for understanding how to intervene into burnout process were discussed