Tree-ring cores (samples) were collected to reconstruct frequency of insect outbreaks in the larch forest of eastern part of Bogd Khan Mountain, Ulaanbaatar, Mongolia. Using tree ring measurements, master chronologies of four conifer species were built. The response functions of Larix sibirica, Pinus sibirica, Pinus sylvestris and Picea obovata chronologies with monthly mean temperature and monthly total precipitation for the interval from 1940 to 2000 showed that their radial growth are mainly controlled by spring precipitation and negatively affected by high summer temperatures. Comparisons of the tree ring chronologies among the four species showed growth suppressions which climate variations and the probable occurrence of insect outbreaks from 1800 to 1900. According the recorded outbreaks, Siberian moth (Dendrolimus sibiricus Tschetw) invasion noted in 1925-1929 and in 1955-1957, vapourer moth (Orgyia antiqua Linn) in 1941-1944, Siberian moth, Jacobsons geometrid moth (Erannis Jacobsoni Djak) in 1971-1972 and Siberian moth and geometrid moths were infested in 1989 in Bogd Khan Mountain, Ulaanbaatar. Recently Siberian moth, vapourer moth and gypsy moth (Ocneria dispar Linn) attacks occurred in 2000, 2003 and 2005 in this region. All these outbreaks reduced radial growth of trees in this region, which were confirmed by this study. Moreover, we identified major disturbances which are most probably linked to insect outbreaks for the years 1902-1903, 1879 - 1880, 1847-1849 and 1825-1829 which may could indicate a roughly 30 year frequency.