Conifer and broadleaf trees emit volatile organic compounds (VOCs). The major components of conifer-derived VOCs are monoterpenes such as α-pinene. We have tried the determination of α-pinene concentration in forest atmosphere. Using 10L gas sampling bag and solid phase microextraction (SPME) fiber as adsorbent, α-pinene concentration was estimated to be 5.2±0.64 (ng/L) (mean±S.E.).