Aqueous ammonia was used to pretreat wheat straw to improve biodegradability and provide nitrogen source for enhancing biogas production. Three doses of ammonia (2%

4%

and 6%

dry matter) and three moisture contents (30%

60%

and 80%

dry matter) were applied to pretreat wheat straw for 7 days. The pretreated wheat straws were anaerobically digested at three loading rates (50

65

and 80 g·L

-1

) to produce biogas. The results indicated that the wheat straw pretreated with 80% moisture content and 4% ammonia achieved the highest methane yield of 199.7 ml·g

-1

(based on per unit volatile solids loaded)

with shorter digestion time (T

80

) of 25 days at the loading rate of 65 g·L

-1

compared to untreated one. The main chemical compositions of wheat straw were also analyzed. The cellulose and hemicellulose contents were decomposed by 2%-20% and 26%-42%

respectively

while the lignin content was hardly removed

cold-water and hot-water extracts were increased by 4%-44%

and 12%-52%

respectively

for the ammonia-pretreated wheat straws at different moisture contents. The appropriate C/N ratio and decomposition of original chemical compositions into relatively readily biodegradable substances will imp

rove the biodegradability and biogas yield.