Abstract: Brittleness is pivotal in predicting shale reservoir quality and designing hydraulic fracturing strategies. However, intricate diagenetic environment of shale, characterized by distinct bedding structures, challenges the isotropic-based brittleness assessment methods. This study introduces a new quantitative approach to assess shale brittleness anisotropy, integrating anisotropic elastic responses and tensile fracturing mechanisms. The proposed model effectively reduces uncertainty in the causal relationship between Young's modulus and brittle failure. Comprehensive experimental validation encompassed 18 samples from six groups of Chang 7 terrestrial shale in Ordos Basin. The optimal anisotropic tensile strength criterion (N-Z criterion, error <5%) was identified, enhancing the theoretical accuracy of the proposed model. Comparative experimental results demonstrate that the model adeptly predicts brittleness strength and directional variation characteristics across variations in mineral type, content and microstructure, underscoring its effectiveness. Additionally, theoretical predictions on shale samples with different organic matter reveal that brittleness strength and its anisotropy across varying OM are not monotonously decreasing. The research highlights that brittleness characteristics are influenced by both mineral type/content and microstructural distribution. Notably, the prevalence of isotropic brittle minerals is the primary determinant of brittleness strength, positively correlated. Conversely, ductile mineral content (striped skeletal support-type OM and clay) negatively correlates with brittleness strength, acting as secondary controlling factors. The impact of pore-filled OM on brittleness appears negligible. Rock physical modeling based on equivalent media theory for shale with pore-filled and/or striped OM further elucidates the mechanisms driving these variations. These findings attach great importance in assessment of terrestrial shale geological and engineering "sweet-spots".