An influence of the alkaline pretreatment of wheat straw with use 0.05M solution of NaOH by 22 hours at 25oC temperature on the effectiveness of anaerobic digestion under mesophilic condition were the subject of this study. The water soaked straw were used as a control. The results showed that alkaline pretreatment improved the solubility of the straw biomass, increasing dissolved COD and concentration of VFA in the feedstock of 10% and 21%, respectively, compared to water soaked samples. Consequently, the cumulative biogas yield was enhanced by 21.5%, reaching 412.1 mL g VS-1 for the pretreated biomass. The digestates were similar in terms of TS and VS, but it significantly differed in terms of phenols concentration which content was considerably higher both in the feedstock as also as in digestate containing alkaline pretreated straw. Initial concentration of phenols in the feedstock of 27 mg L-1 did not block the anaerobic digestion, although its inhibiting effect is forecasted. It was concluded that soaking the straw at low loading of NaOH (4% of raw mass (w/w)) under ambient conditions can efficiently improve its usability for biogas production.