Objectives: This study aimed to identify career support systems for full-time occupational physicians in large companies in Japan with an established company-wide occupational health system. Methods: We conducted interviews with the supervising occupational physicians of target companies selected using the snowball sampling method and that met the inclusion criteria: (1) a company or corporate group with over 10,000 workers; (2) an assigned occupational physician who oversaw occupational physician services for the entire company; and (3) the company had more than 10 full-time occupational physicians. Results: We obtained responses from eight companies (six manufacturing and two railroad companies). All the companies had established a system to support expertise development of occupational physicians, give them greater responsibility, and follow their development in the company. Through the interviews, efforts of each company were described in the following four areas: (1) efforts of human resource development; (2) support for maintaining and improving expertise; (3) treatment in accordance with career stage; and (4) issues related to career support in companies. Conclusions: To provide high-quality, stable occupational health services to an entire company, it is necessary to create a situation where full-time staff can contribute for a long period and develop their careers in the process.