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Sugarcane bagasse (SCB) and trash (SCT) are prospective feedstock materials for fast pyrolysis systems. However, their relatively high inorganic content, especially alkali and alkaline earth metals (AAEMs), affects the quality of the produced bio-oil. In order to overcome this problem, various chemical pretreatment methods have been developed. This study aims to evaluate the effect of demineralization of SCB and SCT on the chemical composition of the bio-oil, viz. by applying micro-pyrolysis (py-GC/MS). Both biomass types were leached with demineralized water, HCl, H2SO4 and citric acid solutions at different temperatures and leaching times. The results indicate that leaching with either inorganic or organic acids, causes the yields of levoglucosan in the pyrolysis vapours to increase. This is explained by the mitigation of undesirable degradation reactions of cellulose and cellulose intermediates in the presence of catalytically active AAEMs, the latter being partially removed in the leaching process. The limited variations in yield of phenolic compounds upon different pretreatments demonstrated the stability of the lignin irrespective any leaching pretreatment. The composition of pyrolysis vapours derived from citric acid-treated biomass is hardly influenced by any changes in demineralization conditions.