This study measured the change of critical thinking skills (CTS) of dental students in a problem-based learning (PBL) pedagogical method. The quantitative analysis was focused on measuring students' CTS achievement starting from their first- through third-year of dental education at the University of Southern California.; This non-experimental study used a cross-sectional design. Evaluation was based on a volunteer sample of 98 dental students who completed a demographics/academic questionnaire and a psychometric assessment known as the Health Sciences Reasoning Test (HSRT) that consisted of 33-item multiple choice format test. The HSRT produced the overall CTS score or the total score. In addition, the HSRT also generated five sub-scales scores relating to CTS: analysis, inference, evaluation, deductive reasoning, and inductive reasoning. Both descriptive and inferential statistical analyses were carried out.; The results of this study concluded that students showed no continuous and significant incremental improvement in their overall CTS score achievement during their PBL-based dental education. Except for the inductive reasoning score, this result was very consistent with other four sub-scales scores as well. Moreover, after performing the statistical adjustment (ANCOVA) on total score and sub-scales scores, no significant statistical differences were found among the three student groups. On the other hand, the results of this study also showed some aspects of critical thinking achievements that differed by categories of gender, race, and English as first language.