In order to elucidate carbon cycling in the forest ecosystem,respiration of soils under deciduous(Quercus acutissima,Acer palmatum Thunberg and Fraxinus rhynchophylla Hance),coniferous(Pinus koraiensis) and mixed(Pinus koraiensis,Quercus acutissima and Acer palmatum Thunberg) forests and its environmental factors were investigated in Kwangneung Experimental Forest,Pochun-gun,Gunggi-do,Korea. In situ soil respiration was being measured for a 16-month period between August 2001 and December 2002 using Pp-systens EGM-4(IRGA). For each measurement,soil temperature,gravimetric water content,soil organic matter content,total organic carbon,total nitrogen and carbon to nitrogen ratio in the subsoil 10cm depth were also determined. Relations between soil respiration and their environmental factors were analyzed,and causes leading to difference between three forests were found out. Results indicated that soil respiration rates from the forest soil were strongly related to soil temperature. The highest correlation was found with the soil temperature at the depth of 10 cm,and soil respiration rates increased exponentially with increase in soil temperature. Thus,soil temperature was the primary abiotic determinant of soil respiration rates in this study. Q₁₀ model was used to figure out the Q₁₀ value of the decidous,coniferous and mixed forest soils,being 3.6(r²=0.66),3.8(r²=0.63) and 3.2(r²=0.63),respectively. The daily mean soil respiration rate was CO₂ 15.12,15.10 and 13.99 g m^-2 d^-1,respectively. No difference was found between deciduous and coniferous forests,but difference did exist between mixed forest and the others. Other than that no environmental factors had any significant effect. However,when temperature was not a limiting factor,soil water content had some effect on forest soil CO₂ efflux. A modeling examination showed in summer(20℃),soil respiration rates increased exponentially with increase in soil water content,whereas in winter(4℃),soil respiration rates decreased exponentially with increase in soil water content. In spring and autumn(10℃),there was no apparent effect of soil water content.