Abstract The aim of this study was to determine changes in crystallinity and crystalline unit cell type of heat-treated Scots pine (Pinus sylvestris L.) and Uludag ˘ fir (Abies nordmanniana stev. subsp. bornmuelleriana Mattf.) wood samples by means of FT-IR spectroscopic method. Heat treatment was applied on the test samples in an oven at three different temperatures (120, 150, and 180°C) and for two different periods of time (6 and 10 h) under atmospheric pressure. It was designated that crystallinity of both Scots pine and Uludag ˘ fir wood samples increased during heat treatment depending on the duration. However, monoclinic structure in crystalline unit cells of Scots pine and Ulu- dag ˘ fir wood samples converted to triclinic structure when heat treated. It was estimated that monoclinic structure was dominant in the crystalline unit cell. It was established that the crystalline structure of Scots pine wood samples was more affected by heat treatment than that of Uludag ˘ fir wood samples. Introduction Wood is subjected to heat treatment for many reasons. Heat treatment of wood contributes to the thermal degradation of its constituents and changes M. Akgu ¨l (&) Æ S. Korkut Du ¨ zce Forestry Faculty, The Department of Forest Industrial Engineering, Abant _ Izzet Baysal University, 81620 Du ¨ zce, Turkey e-mail: akgul_m@ibu.edu.tr; akgulmehmet@yahoo.com E. Gu ¨ mu ¨ skaya Faculty of Forestry, The Department of Forest Industry Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey 123 Wood Sci Technol (2007) 41:281–289 DOI 10.1007/s00226-006-0110-9 ORIGINAL Crystalline structure of heat-treated Scots pine [Pinus sylvestris L.] and Uludag ˘ fir [Abies nordmanniana (Stev.) subsp. bornmuelleriana (Mattf.)] wood Mehmet Akgu ¨l Æ Esat Gu ¨ mu ¨ skaya Æ Su ¨ leyman Korkut Received: 16 June 2006 / Published online: 24 October 2006 Ó Springer-Verlag 2006