The purpose of this study was to investigate the effect of managers’ behavioral biases on strategic decisions. Specifically, this paper examines the impact of, overconfidence, risk aversion, control illusion, and emotional intelligence on the diversification decision. The data were collected from Tunisian managers. It uses a Sample of 111 respondents representing different segments of Tunisian companies. The logistic regression analysis was utilized to control the impact of behavioral biases on decision-making. Findings suggest that managers have different attitudes toward decision-making. While overconfidence and control illusion negatively affect decision making, risk aversion, and intelligence emotions show a positive effect on decision-making. Empirically, the authors' results can serve as a reference for decision-makers to clarify data on the psychological role. Theoretically, the researchers found that the differences between the results are due to the quality of data collection or to the method of evaluation of the decision-making strategy.