Alkaline pretreatment with NaOH was used to improve biogas production from softwood pine. The pretreatments were carried out with 8.0% w/w NaOH solution at two temperatures (0 and 100 degrees C) for different periods of time (10, 30 and 60 min). By anaerobic digestion of the treated and untreated materials to biogas, significant effects of the pretreatments on the yield of methane were clearly observed. The best improvement was achieved by the treatment at 100 degrees C for 10 min, which resulted in 181.2% improvement in the methane production yield. The treatment at 0 degrees C was also effective, in which 60 min treatment resulted in 118.6% improvement in the methane yield compared to the untreated wood. Fourier transform infrared (FTIR) was used to analyze the changes in chemical structure and physical characteristics of lignin, hemicellulose, and cellulose of the treated wood, which indicated a reduction of crystallinity of cellulose due to the pretreatment. Furthermore, scanning electron microscopic images revealed that disruption of the recalcitrant structure of the pine wood could be responsible for the improvement of methane yield. (C) 2013 Elsevier Ltd. All rights reserved.