Acid hydrolysis is used as a treatment method to hydrolyse the polysaccharides present in biomass to fermentable sugar. In this research the hydrolysis of oat bagasse was studied employing different inorganic acids (HCl, H2SO4 and H3PO4) at low temperatures (90 – 110 °C) in a long-term process. Sulphuric acid showed a high potential to produce reducing sugars reaching the maximum production yields at 110°C, while hydrochloric acid at 110°C was the most catabolic acid promoting sugars transformation into furfural. FTIR and relative transmittance analyses suggested that major impact on lignin polymer was made by phosphoric acid hydrolysis at Combined Severity Factors (CSF) higher than 1.5. Kinetic constants calculated from conventional Saeman model allowed to determine thermodynamic parameters for each inorganic acid. Decomposition of sugars occurred most frequently when the Activation Energies (Ae) were low than calculated for sugar production, being aldehydes, the most stable products obtained during hydrolysis. Thermodynamic parameters show and endothermic and non-spontaneous oat bagasse hydrolysis reaction for different inorganic acids.