Several completely stirred tank reactors (CSTR) connected in series for anaerobic digestion of corn stover were investigated in laboratory scale. Serial anaerobic digestion systems operated at a total HRT of 40 days, and distribution of HRT are 10 + 30 days (HRT10 + 30 d), 20 + 20 days (HRT20 + 20 d), and 30 + 10 days (HRT30 + 10 d) were compared to a conventional one-step CSTR at the same HRT of 40 d. The results showed that in HRT10 + 30 d serial system, the process became very unstable at organic load of 50 gTS.L-1. The HRT20 + 20 d and HRT30 + 10 d serial systems improved methane production by 8.3-14.6% compared to the one-step system in all loads of 50, 70, 90 gTS.L-1. The conversion rates of total solid, cellulose, and hemicellulose were increased in serial anaerobic digestion systems compared to single system. The serial systems showed more stable process performance in high organic load. HRT30 + 10 d system showed the best biogas production and conversions among all systems. (C) 2017 Published by Elsevier Ltd.