Purpose: The purpose of this paper is to contribute to the validation of the Organizational Justice Index (OJI) by Hoy and Tarter (2004), a self-report questionnaire for teachers' perceptions of fairness in the operation and administration of schools. Design/methodology/approach: In two studies the authors validated the Italian version of the OJI. Study 1 included 164 Italian high school teachers (76.8 percent were female) to test structure and construct validity. Study 2 involved 200 teachers (permanent and temporary teachers) to confirm the structure of the scale, test the construct and criterion validity, and invariance. Findings: Confirmatory factor analyses confirmed the one-factor solution and that the structure of the scale was the same across teachers. Results revealed high internal reliability. The OJI correlated positively with equity, school climate, and job satisfaction, and negatively with depression and burnout. Research limitations/implications: Since the research approach could lead to common method variance issues, it will be important to determine the associations of OJI with non-self-report assessments. Practical implications: The OJI can be applied optimally to: assess potential organizational problems prior to conducting major interventions; investigate school dynamic problems; target interventions designed to enhance perception of organizational justice; incorporate evaluation of organizational justice as part of regular employee assessments. Originality/value: Overall findings fill the need of standardized measures of organizational justice for specific context. The OJI is a valid instrument to measure organizational justice in school, involving different type of teachers.