Abstract: Brittleness is a key indicator to select favorable fracturing intervals. Mineral-based method and elastic parameter-based method are generally used to evaluate shale brittleness. The marine shales in South China are characterized by various sedimentary environment, complex lithofacies and large range of burial depth. The paper analyzes the theoretical defects and the limitations during application on the basis of case study. Based on the research results on shale mechanical properties, the paper summarizes the influences of mineral composition, organic matter, bedding and confining pressure on shale brittleness, and demonstrates the relationship between brittleness and fracability. The comprehensive analysis shows that mineral-based method is more applicable but has a detect that there is not a unified definition for brittle minerals yet. Elastic parameter-based method can perform logging and seismic prediction effectively, but this method can’t reflect the influence of confining pressure and it is difficult to characterize the brittleness differences between deep and shallow shales with the method. Combined with the lithofacies and burial depth range of marine shales in South China and based on the differences among different mineral components, quartz, dolomite and pyrite are proposed to be considered as brittle minerals; based on the influence of confining pressure on brittleness, the paper suggests that strength or fracture toughness should be added to the elastic parameter-based indices as a confining pressure-indicator to apply to the deep-burial shale brittleness evaluation. Profound understandings on the influences of mineral composition, organic matter, bedding and burial depth on brittleness and the relationship between brittleness and fracability can promote detailed lithofacies characterization of shales and sweep-spot optimization