Purpose@#Self-management of diabetes is a significant challenge. This study aimed to assess diabetes self-care activities and barriers among Korean young adults with diabetes mellitus. @*Materials and Methods@#This study recruited 209 Korean adults with diabetes, with an onset age of 20–39 years, from four university hospitals. Demographic characteristics and the Summary of Diabetes Self-Care Activities (SDSCA) measure and Diabetes Self-Care Barriers Assessment Scale for Older Adults (DSCB-OA) scores were assessed using questionnaires. @*Results@#The average age of study participants was 32.9±6.1 years. Their self-care activities, including adherence to recommended diabetes medication (5.6±2.4) and number of diabetes pills (5.5±2.3) in the SDSCA measure, were the most well-performed activities among all domains. Responses to inspection of the inside of shoes in the foot care activity (0.8±1.5) and specific exercise sessions in the exercise activity (1.6±1.9) reflected poor levels of compliance. According to the DSCB-OA questionnaire, the mean diabetes self-care barrier of DSCB-OA was 20.6±5.0 of total score 45. The greater perceived barriers to self-care on the DSCB-OA were having difficulty exercising regularly (1.9±0.7) and eating three meals and snacks leading to weight gain (1.9±0.8). @*Conclusion@#Young adults with early-onset diabetes showed a greater barrier to regular exercise and poor compliance with foot care and blood sugar testing. Healthcare providers must strengthen their relationship with young adults with diabetes to provide more education and guidelines for lifestyle modification focused on exercise and to promote higher compliance with diabetic self-care activities for improving clinical outcomes.