Forest change in the Korean Peninsula related to different socioeconomic developments in North and South Korea and impacted on the regional environment. However, there was a lack of consistent information about forest changes, especially comparative knowledge of North and South Korea that support management and policymaking. We used the change object update method to generate the first object-based 30m land cover set for the peninsula and analyzed new observations of forest changes in North and South Korea from 1990-2000 to 2000-2015. Results showed that, in North Korea, annual forest loss increased from 142 km(2).yr(-1) to 257 km(2).yr(-1), and the total loss increased from 1,407 km(2) to 3,769 km(2). The elevation range where forest loss concentrated shifted from 100-300 m to 300-1,000 m. The conversion of forest to cropland increased from 1,256 km2 to 3,910 km(2), indicating North Korea's forest eroded by agriculture expansion to ensure food security. By contrast, in SouthKorea, despite forest total loss increased from 338 km(2) to 513 km(2), annual loss remained at 34 km(2).yr(-1). The forest loss was concentrated at the elevation range of 0-300 m, which linked with built-up land expansion. Different public income and social developments drove distinct magnitude of forest loss in the two countries. Follow the Global Forest Observations Initiative, although forest loss might be underestimated for North Korea and overestimated for South Korea, our land change information equipped good overall accuracy (>= 0.94 +/- 0.031). This study could provide useful implications for forest management and regional sustainable development.