Despite the extensive use of marketer generated content (MGC) as a dominating social media marketing tool, marketers haven’t reached a clear understanding about whether MGC has impact on sales and what type of content is effective. In this study, we quantify the impact of social media MGC on product sales and specifically examine the effect of different types of contents, i.e., informative content, persuasive content, and promotional content. Based on a quasi-experiment design, we apply difference-in-differences method on a unique data set with firm MGC activities on a mobile social media platform and the corresponding product sales. We find that MGC has positive and significant effect on product sales. The overall sales elasticity is 51.47%, which means an average 51.47% increase of product sales after MGC marketing. Furthermore, we find that marketing content is a key in generating sales. In general, informative social media marketing content is more effective in stimulating product sales than persuasive and promotional contents. However, such content effect is subject to product categories. Specifically, for sales of highinvolvement products, informative content is more effective, whereas persuasive content and promotional content are more sales effective for low-involvement products. Marketers may develop appropriate social media strategy and design marketing contents accordingly.