Disturbances in the molecular machinery that regulate endolysosomal trafficking lead to osteoclast dysfunction and osteopetrosis: a group of clinically and genetically heterogeneous skeletal diseases that share the feature of high bone mass. Human autosomal recessive osteopetrosis (ARO), also called malignant infantile osteopetrosis, is a severe osteoclast-rich form ARO diagnosed at birth and often lethal within 10-years in untreated patients. Among the genes implicated in ARO, mutations in sorting nexin 10 (SNX10) account for >4% of affected infants. SNX10 is a ‘Phox–homology (PX) domain containing only’ member of the sorting nexin (SNX) family that play essential roles in membrane trafficking via the endocytic pathway. We have identified a patient with a novel mutant, SNX10-R51X, who suffered from severe osteopetrosis and bone marrow occlusion. Consistently, SNX10 knockout mice exhibited severe osteopetrosis and prevented bone loss in collagen-induced arthritic mice. We further demonstrated that SNX10 (-/-) osteoclasts displayed impaired bone-resorption function accompanied by defective F-actin belt formation and integrin β3-Src signalling. The expression of TRAP, CtsK and MMP9 in SNX10 (-/-) osteoclasts was also significantly reduced. Interestingly, the defective function of SNX10 (-/-) osteoclasts was partially restored by adenovirus - mediated SNX10 overexpression, indicative of its potential application in gene therapy for SNX10 deficiency. Further, using bimolecular fluorescence complementation (BiFC) to screen for putative SNX10-interacting partners, we identified that SNX10 interacts with ATG5 and other novel molecules, and co-localizes in the autophagosome pathways. Consistently, knockdown of SNX10 expression leads to impairments in autophagosome maturation and autophagic flux. We propose that SNX10 regulates endolysosome and autophagosome pathways required for effective osteoclast bone resorptive function and bone homeostasis, and thus serves as a novel therapeutic target for osteolysis.