The mainstreaming of climate change adaptation is a key process that embeds adaptation in all sectors’ decision-making processes. In order to achieve successful adaptation, we need a socio-ecological transformation that is enabled by robust decision-making which prioritises adaptation. However, measuring the status of adaptation mainstreaming is quite challenging, and few studies have elucidated differences in adaptation mainstreaming among sectors; we therefore propose an assessment framework that does so. Three dimensions illustrating the pathways of adaptation mainstreaming are suggested: awareness, adaptation readiness and advanced implementation. We identify barriers, opportunities and differences among the three sectors of biodiversity conservation, forest management and water management in South Korea. Our results uncover different pathways to mainstreaming adaptation. Levels of awareness and readiness in relation to risk information, institutional arrangements and the active practical implementation of adaptation measures were found to be highest in the water management sector. In the biodiversity conservation sector, levels of active perception, preparation and implementation of adaptation measures in national sectoral policies were found to be relatively low. We also identify the most common barriers and required resources to mainstreaming adaptation and suggest priority entry points for each sector, including the abundant provision of sector-specific risk information and adoption guideline, awareness-raising on national climate change risk, improvements on organizational support, and reinforcing and the preparation of in-house monitoring and evaluation systems. Overall, this study offers insights into the measurement of adaptation mainstreaming by assessing pathways to successful adaptation. As assessing gaps and progress in adaptation is essential for the facilitation of transformational change, it is critical to examine long-term mainstreaming across diverse sectors.