Ash contents, ash free caloric values and carbon contents of different organs from fifteen species of dominant trees in Xiaoxing′anling forest region were studied by burned quickly to ashes method, measured caloric values method and absorbed CO2 method respectively. The sampling site was located in the south of Xiaoxing′anling Forest Region (128°47′32″ E, 47°13′10″ N). These fifteen species of dominant trees were Pinus koraiensis, Larix gmelinii, Picea jezoensis, Abies nephrolepis, Taxus cuspidate, Quercus mongolica, Betula platyphylla, Betula costata, Tilia amurensis, Phellodendron amurense, Fraxinus mandshurica, Juglans mandshurica, Populus davidiana, Acer mono and Ulmus propinqua. Results showed that ash contents were in the range of 0.60%-1.28% for leaves, 1.00%-2.98% for branch, 0.16%-1.22% for trunk, and 2.15%-6.36% for bark. They decreased in the order of bark, branch, leaves and trunk for all fifteen species of trees, and differences of ash contents were significant among different organs of fifteen species of trees by t test (p < 0.01). Average ash contents of fifteen species of trees decreased in the order of U. propinqua, P. davidiana, Q. mongolica, T. amurensis, P. amurense, B. costata, F. mandshurica, P. jezoensis, A. mono, J. mandshurica, P. koraiensis, A. nephrolepis, T. cuspidate, L. gmelinii and B. platyphylla. Ash free caloric values were in the range of 2085-22.85 kJ/g for leaves, 19.92-21.95 kJ/g for branch, 19.66-21.98 kJ/g for trunk, 18.58-21.74 kJ/g for bark, and decreased in the order of leaves, branch, trunk and bark for fifteen species of trees, and differences of ash free caloric values were significant among different organs of fifteen species of trees by t test (p < 0.01). Average ash free caloric values of fifteen species of trees decreased in the order of L. gmelinii, P. koraiensis, T. cuspidate, P. jezoensis, J. mandshurica, A. nephrolepis, P. davidiana, A. mono, B. platyphylla, P. amurense, F. mandshurica, T. amurensis, Q. mongolica, B. costata and U. propinqua. Carbon contents were in the range of 43.11%-45.08% for leaves, 44.31%-46.06% for branch, 46.30%-47.46% for trunk, 44.31%-45.46% for bark, and decreased in the order of trunk, branch, bark and leaves for fifteen species of trees, and differences of carbon contents were significant among different organs of fifteen species of trees by t test (p < 0.01). Average carbon contents of fifteen species of trees decreased in the order of L. gmelinii, A. nephrolepis, P. jezoensis, P. koraiensis, P. amurense, T. cuspidate, T. amurensis, P. davidiana, B. platyphylla, B. costata, F. mandshurica, J. mandshurica, A. mono, Q. mongolica and U. propinqua. Average ash contents of the conifer trees were lower than the broadleaf trees, and average ash free caloric values and average carbon contents of conifer trees were higher than those of broadleaf trees.