The burnout syndrome has traditionally been identified in the service sector professions, among which is Social Work. In order to determine this syndrome, different measuring instruments have emerged, including the Maslach Burnout Inventory.The main objective of this study was to evaluate the psychometric properties of this instrument and to find evidence of its validity (corroborating the original factorial structure and its convergent validity) and reliability (internal consistency). The Spanish adapted version of the Maslach Burnout Inventory was used. Four hundred social workers participated, randomly divided into two samples of 200 individuals (Sample 1: M = 43.06, SD = 9.04 and Sample 2: M = 40.89, SD = 8.78). We carried out principal components exploratory factor analysis with Varimax rotation.The results identified a factorial structure with four factors (Emotional Exhaustion, Depersonalization, Personal Realization, and Interpersonal Psychological Stress) (χ 2 /df = 1.73, CFI = 0.929, NNFI = 0.859, SRMR = 0.069, RMSEA = 0.061), different from that of the original questionnaire, which indicated three dimensions. The data also show a high internal consistency (α = 0.882). The four factors were directly and moderately associated with each other (r between 0.328 and 0.534). In conclusion, this study provides new data of a valid and reliable tool for evaluating professional burnout or exhaustion.