Background: Little is known about the impact of diabetes mellitus (DM) continuing education (CE) programs on the knowledge, attitudes, and practices of primary healthcare physicians (PHPs) in the Arab world. Accordingly, we aimed to evaluate the effectiveness of a diabetes CE program on the knowledge, attitudes and practices of PHPs in Aseer region, Saudi Arabia. Methods: This was a quasi-experimental study using a pre-test and post-test design. PHPs attended a three-day diabetes CE session and completed a standardized questionnaire before and after the training session. Also, their practices were assessed by reviewing the records of patients with DM before the CE program and three months later. Results: A total of 51 PHPs completed the CE program. The sample had a mean (± SD) age of 33.8 ± 6.0 years, and 72.5% were male. The mean knowledge score increased from 14.33 (± 3.37) to 17.61 (± 2.57) (p < 0.001), and the rate of good knowledge increased from 39 (76.5%) before to 51 (100.0%) after (p < 0.001). There was no significant difference in the mean attitude scores before and after the intervention (3.79 vs 3.86; p = 0.10), respectively. Overall, PHPs' practices related to glycosylated hemoglobin estimation (p = 0.004), foot care (p = 0.02), diet (p < 0.001), exercise (p <0.001), and weight assessment (p < 0.001) significantly improved following the intervention. Conclusion: The CE program for PHPs was effective in addressing knowledge gap of PHPs and in improving their practices towards quality patient care.