Recently, at the end of 2019, the whole world was affected by the outbreak of COVID-19 disease, which has caused massive disruption of the normal teaching and learning process worldwide, including Thailand's educational system. This sudden shift of the educational processes to online learning and teaching has caused many challenges as teachers, learners, and educational institutes are not well-prepared, especially in developing countries like Thailand. This research used a mixed-methods approach, quantitative and qualitative data, in which a google form survey questionnaire was designed in both English and Thai language to (1) investigate Thai students' perceptions of the online learning experience; (2) assess factors that cause challenges in online learning in Thailand; (3) find out strategies for improvement and overcome the challenges. For the sample of the study, 465 students were selected purposively from two public Universities in Thailand due to convenience for collecting data as two co-researchers were teaching in these universities. Results identified major challenges such as the temptation to see other sites, difficulty in understanding the lesson context, poor internet connectivity, difficulty in time management, difficulty in attending the online examination, poor quality of learning experience, low interest/motivation, difficulty in selecting the area at home, difficulty in doing work assignment/task, and distraction at home learning environment. Among the identified factors for these challenges were distraction due to noise and poor learning environment at home, teacher's incompetency due to technical, poor teaching skills, unstructured content or no follow-up, and technological constraint affecting the quality of audio/video uploaded connectivity, technical issue or data limit. Students also suggested strategies to overcome online learning challenges such as improvement in evaluation, connectivity, interactivity, content and accessing materials. The study concluded that all these factors and strategies should be considered for the effective implementation of the online education system in Thailand.