Learner beliefs, anxiety, and motivation are three common learner characteristics. They have consistently been found to account for language learning performance. Meanwhile, self-regulation is critical in sustaining online learners' continuous efforts and predicting their learning outcomes. Despite the massive and rapidly increasing number of online English learners, few studies have clarified the assumed relationships between learner characteristics (learner beliefs, anxiety, motivation) and self-regulation in the online English learning context. This study aims to fill the gap by conducting structural equation modeling analysis to examine their relations. To fulfill the research purpose, we adopted the previous questionnaires with sufficient reliability as instruments to evaluate students' online English learner beliefs, learning anxiety, learning motivation and online self-regulated English learning. The valid responses collected from 425 Chinese undergraduate university students enrolled in an online academic English writing course provided the data source. The results indicated that learner beliefs positively predicted, while learning anxiety negatively predicted, online self-regulated English learning. Online English learning motivation was a mediator in these associations. The findings suggested that stronger learner beliefs of self-efficacy and perceived value of English learning promoted learning motivation and self-regulation. In contrast, higher learning anxiety, such as test anxiety and fear of negative evaluation, harmed learners' motivation and their online self-regulated English learning.Sustainability 2020, 12, 3009 2 of 25 integrate cognitive, affective and behavioral factors, so as to achieve a continuous learning outcome. Among these, learner beliefs, anxiety, motivation and self-regulation are intensively studied [1][2][3][4][5][6][7].Three learner characteristics are commonly and consistently found to account for foreign language learning performance, namely learner beliefs, anxiety and motivation [7][8][9][10]. To be specific, language learning beliefs are critical because they impose strong impacts on how students evaluate and utilize language learning strategies. Language learners, for instance, may hold different opinions on what accounts for a successful foreign language learning. Some think learning English grammar and vocabulary is the major task, while others contend that it is important to use and speak English in an appropriate language environment [11]. Foreign language learning anxiety includes uncomfortable feelings in using or learning a foreign language. Such anxiety is common among Chinese English-as-a-foreign language (EFL) learners with different proficiency levels. Most English learners, especially for those at beginner levels, feel more anxious when they are singled out to speak English or use English to respond to the teacher in class. English learners with a higher level of foreign language anxiety may form a mental block which greatly hinders foreign language learning e...