This study investigated biogas production as an alternative treatment of tannery wastewater (TWW) and its use as a pre-treatment medium to increase CH4 yield from anaerobic digestion (AD) of wheat straw. The TWW had high levels of sulfate and chloride, so biochemical CH4 potential could be estimated only when the TWW was diluted. Untreated straw yielded 255 NL CH4 (kg VS)(-1), whereas straw that had been pre-treated with TWW yielded 314 NL CH4 (kg VS)(-1) (35% increase). Treatment of TWW by AD with a co-substrate might be possible using a controlled feedstock mixing ratio. Use of TWW as a pre-treatment medium by simple co-storage before AD would be beneficial as an inexpensive treatment of lignocellulosic biomass.