Continuous biological treatment of paperboard mill wastewater under changes of organic loading rate (OLR) along with hydrogen production was investigated. The continuous experiments were conducted at different OLRs from 1.2 to 18.6kg COD/L.d. The COD removal efficiency increased from 30.8±3.1 to 83.6±5.3% with decreasing OLR from 18.6 to 1.2kg COD/L.d, respectively. TSS, VSS, and carbohydrates removal efficiencies were 86.5±5.11%, 81.6±1.7%, and 63.5±19%, respectively. Meanwhile, the hydrogen production rate was amounted the highest value of 4.74±0.9 L/d at OLR of 9.3kg COD/L.d which coincided to the highest volatile fatty acids of 337±13.6mg/l and HAc/HBu of 2.13±0.4.