This empirical study explores metacognition and its relationship with writing performance. Through multivariate analyses, the study investigates the role of metacognitive knowledge and regulation in mediating writing performance. Participants were 882 students from eight universities in China who were learning English as a foreign language (EFL). Results reveal that scores on six parameters of metacognition (declarative knowledge, procedural knowledge, conditional knowledge, planning, monitoring, and evaluating) were positively correlated with EFL writing performance. Parameters of procedural knowledge, planning, monitoring, and evaluating were more highly correlated with writing compared with other parameters. Results also revealed that scores on metacognitive regulation can play unique roles in predicting writing proficiency over and above prediction based on scores on metacognitive knowledge. These findings underscore the importance of enhancing metacognitive regulatory skills for university EFL learners' writing performance.