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The purpose of this study is to investigate the rationality of behavioral economics in mental accounting by studying laboratory economics. Undoubtedly, economic man, whose fundamental characteristic is rationality, is the starting point for economic analysis. In conventional economics, the premise of rationality is the cornerstone and the premise of all economic theories. However, critics of economic rationality argue that economic agents sometimes exhibit irrational behaviors that may be limited by mental capabilities. Behavioral economics, which is generally based on abstract preferences, addresses the general frameworks of subjective accounting. In this study, an economic experiment was designed by providing a laboratory environment and using thirty actors. Laboratory economics assesses behavioral assumptions and theories by means of controlled experiments. The results indicate that there is a significant relationship between the rationality of economic behavior and mental accounting. This study argues that it is not possible to provide a realistic analysis of individuals' financial behaviors only on the assumption of rationality and without considering other factors, particularly the behavioral constraints of decision makers. Given the limited number of studies of behavioral economics, the present study can help us to better understand financial behaviors of mental accounting origin.