E-commerce is pressured to always provide better service amidst severe business competition. One popular way to achieve it is through exploiting customers' data. Despite its benefits, using customers' data may results in privacy violation that leads customers to build higher fences to protect their privacy. In order to maintain the optimal benefit of using customers' data, first, we need to address the determinant of customers' online privacy concern. Hence, this study performs an empirical study of 1, 017 respondents using CB-SEM approach to understand the phenomenon from the perspective of different gender. The result shows that internal factors affecting online privacy concerns in e-commerce are privacy awareness, previous online experience, and privacy control, while the external factor is information collection. Additionally, result shows that each gender has different contributing factors in online privacy concern. Meanwhile, online privacy concerns have a significant role in triggering defensive behaviour in customer such as withholding personal information and fabricating personal information.