The effects of the treatment of corn stover with sodium hydroxide (NaOH) on its digestibility and biogas production was studied varying the initial stover-treatment time (3 days and 6 days), temperature (10, 20, 30, and 50 degrees C), and moisture level (50, 75, 85, and 90%). The degradation rates of hemicellulose, cellulose, and lignin increased with the increasing treatment time, temperature, and moisture content. The highest biogas and methane yield were 420.6 and 233.0 mL/g VS achieved by the stovers treated at 20 degrees C and moisture level of 90% for 3 days. The results showed that the ambient temperature (20 degrees C), moisture level of 90%, and three days pretreatment could be recommended.