Modular Object-Oriented Dynamic Learning Environment (Moodle) is an open source Learning Management System (LMS) receiving more and more popularity in higher education. Many academic departments in colleges and universities employ Moodle to economically improve course management. English as Second Language (ESL) programs in universities have also adopted Moodle. However, successfully implementing Moodle in ESL courses requires ESL students to accept the system. The Unified Theory of Acceptance and Use of Technology (UTAUT) model was used as a framework to investigate the factors influencing ESL college students' acceptance and use of Moodle in their English classes. Additionally, this study aimed at representing ESL college students' perspectives on what factors impacted their acceptance or rejection of Moodle. Thirteen ESL college students participated in this study, and four focus group discussions were conducted. Participants expressed five major factors that influenced the adoption of Moodle in ESL grammar and reading classes. These factors were performance expectancy, effort expectancy, social influence, facilitating conditions, and former practice. The participants attribute Moodle for improving their study efficiency and learning skill, providing them with multiple learning resources and giving them emotional motivation. This performance expectancy was the most important reason for them in adopting Moodle. They cited Moodle's ease of use, or effort expectancy, as the second significant reason for adoption. Additionally, social influence and facilitating condition were considered supplemental factors influencing their acceptance of Moodle. Besides these four constructs in the UTAUT model, some participants proposed that former practice, or their experience with Moodle or other learning management systems, enabled them to adopt Moodle more quickly. The findings provide beneficial suggestions for educational administrators and course management developers who have interest in using Moodle to teach English courses to ESL students.