Study Objective: The main objective of the study is to measure the impact of the joint audit on the rationalization of investors' decisions by applying to companies listed on the Egyptian stock Exchange during the period from 2018 to 2023. Design and Methodology: The study relied on appropriate statistical models for analyzing Panel Data using the statistical program Stata/IC 15, which combines Cross-sectional Data and Time Series Data approaches, for a sample of (73) non-financial companies registered on the Egyptian Stock Exchange during the period from (2018 to 2023), to build an empirical model for testing the study hypothesis that reflect the impact of joint audit on rationalizing investors' decisions. Results and recommendations: The results of this study indicate that joint audit has a positive and significant impact on rationalizing investors' decisions. Based on this, the study recommends that the relevant authorities and regulators of the auditing profession in Egypt should adopt a standard for joint audit and impose severe penalties in case of any agreement between the two audit firms participating in the joint audit process in a way that makes it a fictitious process and turns it into an individual audit. Originality and Addition: The current study is considered one of the important studies in the Arab environment in general, as it contributes to the accounting literature by attempting to reduce the controversy regarding the relationship between joint audit and investors' decisions. This study is considered one of the rare studies that directly addressed the impact of joint audit on investors' decisions in the Egyptian business environment, as an example of emerging economies. Keywords: Joint audit, investors' decisions.