The purpose of this study was to determine effects of Mindfulness-Based Cognitive Therapy(MBCT) in an online video conferencing method(ZOOM) for adult siblings on individuals with developmental disabilities. For this study, the mindfulness-based cognitive therapy (MBCT) developed by Segal et al. (2002/2006) was modified in consideration of characteristics of the participants, It was reorganized with an online video conference (ZOOM) due to COVID-19 situation. Study participants were adult non-disabled siblings aged 19-35 years of those with developmental disabilities. They recruited through the Support Center for the Developmental Disabilities, the Family Support Center for the Disabled, Social Welfare Centers, and the Special Education Department of the university. There were a total of 27 participants in the initial study. Due to schedule changes or loss of contact, 21 participants were included in the final analysis. The MBCT program was conducted with 8 sessions(twice a week) of online video conferencing (ZOOM). After the MBCT program intervention was given to the participant group, changes were compared between the participant group and a control group according to the timing of previous, post, 4-week-follow up measurement. Based on collected data, a chi-square test and an independent t-test were performed and a mixed two-way repeated measures ANOVA was performed to verify the effectiveness of the program. When the interaction between group and period was significant, interaction contrasts were tested to verify at what point in time the interaction appeared. As a result of this study, it was found that the MBCT program had a significant effect in increasing the level of mindfulness and reducing depression. Based on results of this study, the significance and limitations of the study and suggestions for further research were discussed.