Downed log is a conspicuous and important component of forest ecosystems. The CO2 flux from downed logs (RCWD) is an important component of carbon budgets in forest ecosystems with moderate to large amounts of downed logs. In this study, we used an infrared gas exchange analyzer (LI-6400 IRGA) to measure the RCWD of 11 major tree species in natural secondary temperate forests in northeastern China and related environmental factors. Our specific objectives were to (1) compare RCWD, temperature (TCWD) and water content of downed logs (WCWD) for the 11 tree species；(2) quantify the relationships of RCWD against TCWD and WCWD for the species; and (3) examine seasonal dynamics of RCWD. The measured RCWD for Betula platyphylla, Populus davidiana, Tilia amurensis, Juglans mandshurica, Quercus mongolica, Acer mono, Ulmus propinqua, Pinus koraiensis, Phellodendron amurense, Larix gmelinii, and Fraxinus mandshurica averaged 10.64, 8.38, 7.85, 6.59, 6.01, 4.07, 3.88, 2.55, 2.29, 1.96 μmolCO2•m^-2•s^-1 and 1.90μmolCO₂•m^-2•s^-1, respectively. The RCWD for the softwood tree species was greater than that for the hardwood tree species, and the RCWD for the coniferous species tended to be less than that for the broadleaved species. During the measuring period, the TCWD did not differ significantly among tree species (p > 0.1), but the WCWD did (p < 0.001). The RCWD was significantly affected by tree species, dimension of downed logs, site conditions, and their interactions, but the degree of these effects depended on tree species. The TCWD, WCWD and their interactions significantly (p < 0.01) influenced the RCWD, explaining 39.9%~72.9% of the variations in the RCWD data. The seasonality of RCWD was mainly driven by the TCWD and showed an overall bell-shaped curve for all the tree species, whereas the variations among tree species within a specific season were mainly influenced by WCWD.