Learner autonomy has received growing interest from researchers and educators since the 1980s. Autonomous learners are supposed to monitor their progress and assess their performance. The present study investigated the effects of learner factors on the scorer reliability of self- and peer-assessment of EFL (English as foreign language) writing among Chinese college students. The learner factors involved are second language (L2) proficiency and English self-concept. The experiment was conducted on 52 Chinese college students. The results show that: 1) Though L2 proficiency had a limited effect, high-achievers seemed to perform better in self- and peer-assessment to some extent; 2) high English self-concept led to a higher reliability of self-assessment; and 3) on the whole, the subjects' self-assessment was more accurate than peer-assessment, but they tended to overestimate their own performance while underestimate their peers' regardless of their L2 proficiency and English self-concept.