Purpose: In 2015, the South Korean government legislated the Act for the Improvement of Training Conditions and Status of Medical Resid7`nn78bbbbbbbbbbnbents (Medical Resident Act). This study investigated changes in the working and learning environment pre- and post-implementation of the Medical Resident Act in 2017, as well as changes in training conditions by year post-implementation.Methods: An annual cross-sectional voluntary survey was conducted by the Korean Intern Resident Association (KIRA) between 2016 and 2019. The learning and working environment, including extended shift length, rest time, learning goals, and job satisfaction, were compared by institution type, training year, and specialty.Results: Of the 55,727 enrollees in the KIRA, 15,029 trainees took the survey, and the number of survey participants increased year by year (from 2,984 in 2016 to 4,700 in 2019). Overall working hours tended to decrease; however, interns worked the most (114 hours in 2016, 88 hours in 2019; P<0.001). Having 10 hours or more of break time has gradually become more common (P<0.001). Lunch breaks per week decreased from 5 in 2017 to 4 in 2019 (P<0.001). Trainees’ sense of educational deprivation increased from 17.5% in 2016 to 25.6% in 2018 (P<0.001). Awareness of tasks and program/work achievement goals increased from 29.2% in 2016 to 58.3% in 2018 (P<0.001). Satisfaction with the learning environment increased over time, whereas satisfaction with working conditions varied.Conclusion: The Medical Resident Act has brought promising changes to the training of medical residents in Korea, as well as their satisfaction with the training environment.