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Abstract: The conversion of sunflower oil cake (SOC) into methane by mesophilic anaerobic digestion was the object of this study. The effect of a combined dilute acid-thermal pretreatment (acid concentration and temperature) on solubilisation and methane potential was investigated using a central composite design (CCD). For temperatures up to 170°C, solubilisation of each parameter (total organic carbon, sugars and proteins) increased with the severity of the pretreatment (high temperature and high acid concentration). Methane production was higher for pre-treated samples than for the untreated samples (195mL CH4/gVS). The highest yield (302±10mL CH4/gVS) was obtained after acid pretreatment at 170°C. At this temperature, acid concentrations lower than 1% had no significant impact on methane production in comparison to thermal treatment alone. The volume of methane produced by the soluble fraction reached more than 60% of total methane production. An increase in methane production was correlated to the concentration of organic carbon in the liquid phase of samples pretreated at 130–170°C with acid. At temperatures higher than 170°C, some recalcitrant compounds were formed in the liquid phase. [Copyright &y& Elsevier]