In this study we analyze the relationship between the degree of internationalization and the cumulative abnormal returns of Turkish manufacturing companies listed in BIST 100 Stock Index. Companies choose to internationalize their activities in order to increase their sales volume and by diversifying their markets internationally they can reduce their operational/business risks. In this context, the degree of internationalization of Turkish manufacturing companies were measured as the ratio of their foreign sales revenues to total sales. According to panel data regression results for 2007-2016 period, there is a statistically significant positive relationship between the degree of internationalization measure and the cumulative abnormal stock returns. On the other hand, this relationship disappears when companies are grouped according to their degree of internationalization as low versus high internationalized.