E-Commerce is playing a more significant part in the Indonesian economy. (Rashidirad, Salimian, Soltani, & Fazeli, 2017) shows that an e-business without a clear competitive strategy is very unlikely to outperform; so that in order to succeed in the increasingly competitive environment of e-business, firms would need to carefully develop and implement successful competitive strategies. Competitive advantage grows fundamentally out of value a firm is able to create for its buyers that exceed the firm's cost of creating it. There is a general stream of strategy research that assesses strategy and firm performance (Dess & Davis, 1984; Fahey & Christensen, 1986; Miller & Cardinal, 1994; Kim & Lim, 1988). Considering its nature and objectives, the case study method will be considered as a suitable method for this research. The paper suggests that although cost leadership strategy is able to generate greater performance, pursuing a differentiation strategy can be more worthwhile and sustainable for e-commerce companies compared to cost leadership strategy. This research contributes to existing research by suggesting Porter's generic strategies as a valid and viable model for pure online firms which operate in the current e-business environment.