Sugarcane is a source of roughage in animal feeding. It presents high production per unit of cultivated area, relatively easy cultivation and low cost of production per hectare, and better quality and a high dry matter (DM) yield in periods when forage is scarce. This study aimed to evaluate the effect of increasing levels of calcium hydroxide (Ca(OH)₂) in sugarcane forage on chemical composition, in vitro digestibility values of DM, neutral detergentfibre (NDF) and acid detergent fibre (ADF), and kinetics of thermal decomposition processes of weight loss and heat flow. Sugarcane was collected close to the ground and 50-kg heaps of the fresh material were formed and mixed with four doses of Ca(OH)₂ (0, 8, 16 and 24 g kg^–1 sugarcane). Concentrations of NDF and ADF decreased linearly with increasing amount of Ca(OH)₂, whereas concentration of hemicellulose increased linearly. In vitro digestibilities of DM, NDF and ADF were enhanced in a quadratic manner with increasing amounts of Ca(OH)₂. The release of heat, measured by ΔH, increased linearly with increased Ca(OH)₂ levels, likely due to enhanced digestibility of the fibre components. Weight loss decreased linearly between 272.2°C and 397.7°C with increased amounts of Ca(OH)₂ added to sugarcane, likely due to changes in cellulose structure, which became denser and thermodynamically more stable than native cellulose following the alkaline treatment. Calcium hydroxide changed chemical composition and digestibility of the fibrous fraction of sugarcane, resulting in better nutritional value. The greatest release of heat and highest in vitro digestibility of fibre were observed when adding 15.2 g Ca(OH)₂ kg^–1 sugarcane; therefore, this dose is recommended to enhance the nutritive value of sugarcane as ruminant feed.