The expanding use of social media has the potential to enhance the quality of English as a foreign language (EFL) instruction and learning. The purpose of this online survey-based study was to investigate the mediating effects of intrinsic and extrinsic motivation for reading English social media text among 348 Chinese undergraduate EFL learners. PLS-SEM analyses revealed a significant relationship between the extrinsic motivation to read English text on social media and English language performance. In addition, the extrinsic motivation was also found to significantly mediated the relationship between English reading self-efficacy and English language performance. The findings indicate that in the context of reading English text on social media amongst Chinese undergraduate EFL learners, extrinsic motivation rather than intrinsic motivation mediates the relationship between English reading self-efficacy and English language performance, implying the potentials to use social media as an instructional medium to improve EFL teaching and learning outcomes in China.