During the production of kraft dissolving pulp a pre-hydrolysate stream is generated prior to pulping. This pre-hydrolysate is a potential feedstock for the production of high value-added bioproducts. It contains a considerable amount of dissolved organics such as hemicelluloses, lignin and acetic acid. The purpose of this study was to investigate the effect of sulfur dioxide (SO2) used during the pre-hydrolysis step on furfural production. The production of furfural from two types of simulated kraft dissolving pulp mill pre-hydrolysates was investigated. The first pre-hydrolysate was generated using hot water (PHLW) while the second one (PHLS) was generated using an aqueous solution containing sulfur dioxide (SO2). The effect of temperature and sulfuric acid concentration on furfural yield from both pre-hydrolysates was investigated. A maximum furfural yield of 83.3% was obtained at 240 degrees C and with no sulfuric acid addition when PHLS was employed. For PHLW, a maximum furfural yield of 75.7% was obtained at 240 degrees C and with 3.6 kg m(-3) of sulfuric acid. The higher furfural yield obtained after SO2 pre-hydrolysis step was a result of lignin sulfonation that rendered the lignin less reactive towards intermediate molecules, sugars or furfural during the course of furfural production.