During the COVID-19 crisis, universities worldwide were forced to shift from face-to-face instruction to online instruction. This shift exposes learners to challenges they have never encountered, and numerous studies have revealed a variety of barriers preventing learners from achieving learning goals in an online learning environment. Accordingly, there is an increasing need to understand the factors that contribute to learner success. This study therefore analyzed the key success factors that could assist learners in learning more efficiently in an online learning environment. The participants of this study were 105 Thai learners who were in their second year of an undergraduate degree. To reach the objective of this study, two distinct data collection procedures were used: a questionnaire for learners to identify the factors effecting learners' success in an online course and a focus group interview. The result indicated that teacher support, interaction during learning, and technological support are all critical for the success in online learning.