To optimize the pretreatment conditions, rice straw was treatedat different conditions (concentration, time, solid loading). Thecomposition of untreated and pretreated straws was analyzed, andthe results are summarized in Table 1. All compositional data arebased on the extractive free basis, as rice straw used in this studycontained less than 1% extractive. As can be seen, the untreatedstraw is mainly contained glucan (44.8 wt%), xylan (20.8 wt%),and lignin (18.3 wt%). All pretreatments reduced the lignin andash contents of rice straw (Table 1). In most cases, by increas-ing the pretreatment time and liquid to solid ratio, more ligninwas removed which led to a considerable increase in glucan per-centage (49.5–57.6%). Beside significant lignin removal, sodiumcarbonate pretreatment at 100◦C was succeeded to eliminate morethan 90% of silica from rice straw. Results of this research can be compared with those obtained from sodium hydroxide treatmentof sweet sorghum bagasse in which the lignin content of bagassewas reduced from 18.3 to 12.5% (Goshadrou et al., 2011).