<p>Employee performance remains a critical concern for organisations, particularly when undermined by unethical behaviour and unsupportive cultural environments. Such conditions often diminish productivity, work quality, and organisational commitment. Grounded in social learning theory and social exchange theory, this study investigates the mediating role of appraisal fairness between the relationship of ethical behaviour and employee performance, while examining the moderating influence of organisational culture. Data were collected from 355 employees of Bauchi State Teachers Service Commission and analyzed using SPSS for descriptive statistics and SmartPLS 4.0 for structural equation modeling. The findings revealed that ethical behaviour significantly enhances employee performance, with appraisal fairness partially mediating this relationship. However, organisational culture did not moderate the link between ethical behaviour and performance. These results signify the importance of fair appraisal systems in boosting ethical behaviour and improving performance outcomes. The study contributes to the literature by integrating fairness perceptions into the ethical behaviour performance nexus and offers theoretical and practical guidance to enhance employee engagement and effectiveness in an organisation.</p>