This paper focuses on quality assurance in language massive open online courses (LMOOCs). It is a qualitative study that adopts the grounded theory method and analyses evaluative comments on the quality of LMOOCs from learners' perspectives. With the data collected from 1,000 evaluations from English as a second language (ESL) learners on China's biggest MOOC platform "iCourse", this study examines what has influenced learners' perceptions of LMOOCs and identifies the specific quality criteria of five types of them, including ESL courses for speaking, reading, writing, cultural studies, and integrated skills. The results of the study will lay a foundation for the establishment of a quality criteria framework for LMOOCs and provide insights into design principles for effective online language courses tailored to the diverse needs of a massive number of language learners.