Objective: Reducing treatment dropout in gambling disorder is a critical clinical challenge. Despite the high treatment dropout rates in gambling treatment, research exploring the factors influencing this issue remains limited. This study analyzed sociodemographic characteristics, problem gambling severity, and readiness and commitment to change by comparing treatment dropout and treatment completion groups among gamblers who presented to gambling treatment centers. Method: Participants were 979 adult South Korean men who engaged in illegal online gambling (M = 32.34 years; SD = 6.70) and sought treatment between 2015 and 2023. Baseline assessments included sociodemographic characteristics (e.g., age, marital status, debt), problem gambling severity (Problem Gambling Severity Index), and The Stages of Change Readiness and Treatment Eagerness Scale - Gambling, including the subscales of Recognition, Ambivalence, and Taking Steps. Results: A total of 160 participants (16.3%) completed treatment. Readiness and Commitment to Change showed significant differences between the groups. The dropout group reported higher ambivalence (M = 10.43; SD = 3.53) compared to the completion group (M = 9.89; SD = 3.07; p = .05), while the completion group scored higher on taking steps (M = 29.51; SD = 6.92) than the dropout group (M = 27.95; SD = 7.47; p = .01). However, the analysis revealed no significant differences in sociodemographic characteristics or problem gambling severity. Conclusions: These findings suggest that clearly assessing readiness and commitment to change at the initial stage of treatment for individuals with problem gambling, and providing tailored interventions accordingly, are critical factors in enhancing long-term treatment retention and recovery potential.