The study investigated whether there exists a relationship between unethical behaviour and corporate performance in the university system, and hence determined the impact of unethical behavior on corporate performance in the Nigerian university system with private universities as reference. A survey design was employed with a questionnaire instrument administered to 250 university staff drawn from four private universities in South-west, Nigeria, using a combination of purposive and random sampling techniques. The response data were analyzed using both descriptive and inferential analysis. The descriptive analysis showed that unethical behaviour exists in Nigerian private universities. A multivariate Partial Least Squares Structural Equation Model (PLS-SEM) was used for the inferential analysis and to specify the relationships among the construct variables in the study. The bootstrapping technique of the PLS-SEM was used to estimate the parameters in the model, with the aid of the Smart-3 software. The result of the factor loadings, reliability test, convergent and discriminant validity revealed that the construct variables are fit for the PLS-SEM. The path analysis revealed that financial malpractices are a major unethical behavior affecting corporate performance adversely. Furthermore, unethical behaviours from university staff and university administration have significant negative influence on corporate performance. The study concludes that unethical behaviour is a key driver of poor corporate performance in the Nigerian university system. Therefore, it is recommended that policy makers in the university should adopt a holistic approach to ethical management that is oriented toward zero tolerance for unethical behavior in the university system