The problem-based learning (PBL) is increasingly used in undergraduate education. However, the application of integrated PBL to medical undergraduate education has not been well assessed. An observational study was designed to compare integrated PBL combined with lecture-based classroom (LBC) with traditional LBC teaching in 2 semesters of a Medical School in China. This study was conducted from March 2021 to July 2022. A total of 118 undergraduates majoring in clinical medicine were randomly allocated in 2 groups, 1 group receiving the integrated PBL + LBC teaching (experimental group, n = 60) and another group receiving LBC teaching (control group, n = 58). The experimental group attended the integrated PBL courses for the basic and clinical medicine conducted in the 6th and 8th semesters, respectively, as well as taking the LBC courses. The experimental group was required to preview the course materials before class, make presentations in class and take online feedback questionnaires after class, while the control group was required to preview the textbooks and listen to the traditional LBC courses. The students’ scores of these 2 groups were compared, and feedback questionnaires were performed to evaluate the effectiveness of the experimental group over the control group. Results showed that the experimental group scored significantly higher than the control group in Clinical Skills (95% confidence interval [CI] 4.19–5.89), Internal Medicine I (95% CI: 1.85–9.93), Internal Medicine II (95% CI: 8.07–15.90), Introduction to Surgery (95% CI: 5.08–10.25), Surgery (General Surgery) (95% CI: 7.82–12.72), Surgery (Specialty) (95% CI: 6.47–9.97), and Clinical Medical Level Test (95% CI: 1.60–5.15) (all P < .01). In the feedback questionnaires of integrated PBL, up to 80% and 90% of students were satisfied with the teaching methods and lecturers, respectively. More than 80% of students agreed that the integrated PBL improved their abilities to learn independently, understand knowledge, and to raise, analyze and solve problems. In terms of stress in and out of class, a small number of students, <36.7%, felt stressed. The integrated PBL combined with LBC is an effective teaching approach, which may provide new ideas for teaching research and reform on undergraduate medical education in clinical medicine specialty and other medical majors.