Some of today’s most popular social computing systems are online communities, relying on various types of user-generated content, e.g. YouTube or Instagram. Compared to such traditional on-demand content communities, the recent phenomenon of social live streaming platforms has introduced a fundamentally different way how user-generated content is contributed and consumed. Live streaming platforms enable their users to broadcast and watch video content in real time, while facilitating social interaction by providing complementary interaction features, e.g. chatrooms. As the attraction of user-generated content is crucial for the success of content communities, prior research has examined users’ motives for contributing to various types of on-demand platforms. However, content contribution on social live streaming platforms has been underexplored so far. We address this research gap by examining content contribution on social live streaming platforms by drawing on motivational factors from prior research and applying social capital theory as a theoretical lens. Our empirical analysis is based on web survey data of 543 broadcasters of the market-leading social live streaming platform Twitch. The results show that, while the volume of content contribution is mainly influenced by individual motives, the intention to continue contributing content is primarily affected by a broadcaster’s social capital.