Moodle is applied as an online learning management system in the Faculty of Medicine, Thammasat University (TU), where the curriculum has been based on problem-based learning (PBL) since 2015. Little research on the effectiveness of Moodle and students’ attitudes during their studies at the pre-clinical medical level within a PBL curriculum has been conducted. Hence, this cross-sectional study focuses on second- and the third-year (MD-2 and MD-3) preclinical medical students’ attitudes towards Moodle and its effectiveness in the PBL curriculum by (...) using a 27-itemed self-constructed online questionnaire. Additionally, students’ preferences as regards the materials managed by the Moodle platform were also evaluated as students’ preferred behaving style (SPBS). After obtaining ethical approval from the Human Ethics Committee of TU No. 1 (Faculty of Medicine), the data was collected and analyzed by medians and inter-quartile ranges, Mann-Whitney U test, and Spearman correlation (ρ). After analyzing the data, the results indicated the following: (1) the top four attitudes scores, (2) the two lowest-attitude scores, (3) the top five effectiveness scores (Ef), (4) the three lowest effectiveness scores, and (5) the top three SPBS scores. Interestingly, a stronger positive Spearman’s correlation (ρ) between ‘Prefer doing quizzes in Moodle to in classroom’ and ‘Moodle enhances learning capability’ was found for MD-3 compared with MD-2. This study reports that Moodle is preferable as a platform supporting students’ self-learning within a PBL curriculum. However, to use the Moodle platform to the highest benefit, instructors need to upgrade its capabilities, especially in the area of student-teacher interaction and the enhancement of students’ critical thinking and creativity, as demonstrated by the lowest scores obtained in this study. (shrink)