Forest soils mixed with organic matters (green needle, flesh needle litter and needle litter in F layer of Pinus koraiensis, and green leaf of Quercus dentata and Q. variabilis) were incubated under a constanl: 30℃ (±1) for 53 days to measure the changes of inorganic nitrogen and CO₂ evolution rate. The results obtained were summarized as follows;1) In the early incubation period the amounts of total inorganic nitrogen in soils by mixture of organic matters decreased rapidly because of immobilization by microbial uptake, and thereafter their amounts increased with further incubation, 2) The rate of immobilization of organic nitrogen in mixed organic matters was the highest in green needle among green needle, flesh needle litter and needle litter in F layer of P. koraiensis, but lower than that of green leaf of Q. variabilis and Q. dentata. 3) The rates of CO₂ evolution from soils mixed with organic matters increased sharply in the early time, and then decreased slowly with increasing time. The order of the CO₂ evolution rate was green leaf of Q. variabilis $gt; green leaf of Q. dentata $gt; green needle of P. koraiensis $gt; flesh needle litter of P. koraiensis $gt; needle litter of P. koraiensis in F layer from the largest to the least. 4) Nitrate nitrogen concentrations showed a tendency to increase throughout incubation time, so that their concentrations after 53 days were higher than that of ammonium nitrogen.