<p>Brittleness is a crucial mechanical property of rock, closely related with rock burst disaster. Numerous brittleness indexes have been proposed from various perspectives to predict the rock burst. Among these, indexes based on strain–stress curves are the most widely used, but still face some challenges in calculation and application. This study presents an improved rock brittleness index (BE) by considering the relationships between damage stress (strain), peak stress (strain), and residual stress (strain) derived from complete stress–strain curves. Based on the compression tests of granite, gneiss, quartzite and schist under uniaxial conditions as well as gneiss under triaxial conditions, the BE index was calculated and compared with previously published indexes. The result showed that BE index exhibits a good consistency with stress–strain response and failure morphology, even maintains a linear correlation with fracture surface fractal dimension under triaxial compression conditions, demonstrating superior reliability and accuracy of BE in rock brittleness evaluation. Additionally, the relationship between the BE index and mineral content of the rock was investigated. The results revealed that the total content of ductile minerals exhibits a stronger linear correlation with rock brittleness than brittle minerals content, suggesting that ductile minerals play a more significant role in reducing rock brittleness than brittle minerals do in enhancing it.</p>