Plenty of high-resolution paleoclimate investigations of the last thousand years were carried out to potentially predict future climate changes. Mountainous ombrotrophic peatland is one of the best recorders for high-resolution paleoclimate studies in the forest area. Grain size analysis was carried out on ombrotrophic peat proffle in the eastern mountainous region of Jilin Province, Northeast China. The peat proffle lasts the past 2 000 a by four radiocarbon (AMS14 C) ages. The results showed that the inorganic minerals in the peat proffle are mainly silt, with some contribution from clay and a minor amount of sand, which are mainly due to wind dust and suspended transportation. Two paleoclimate stages are found in this peat proffle by phytolith analysis, peat cellulose isotope research and historical documents: ca. 45–1550 AD, relatively cold period; ca. 1550 AD–present, relatively warm period. This ffnding is important for the initial study of paleoclimatic changes over the last 2 000 a in the mountainous area of eastern mountainous area, Jilin Province, Northeast China.