We have identified a new role for the matrix enzyme lysyl oxidase–like-2 (LOXL2) in the creation and maintenance of the pathologic microenvironment of cancer and fibrotic disease. Our analysis of biopsies from human tumors and fibrotic lung and liver tissues revealed an increase in LOXL2 in disease-associated stroma and limited expression in healthy tissues. Targeting LOXL2 with an inhibitory monoclonal antibody (AB0023) was efficacious in both primary and metastatic xenograft models of cancer, as well as in liver and lung fibrosis models. Inhibition of LOXL2 resulted in a marked reduction in activated fibroblasts, desmoplasia and endothelial cells, decreased production of growth factors and cytokines and decreased transforming growth factor-β (TGF-β) pathway signaling. AB0023 outperformed the small-molecule lysyl oxidase inhibitor β-aminoproprionitrile. The efficacy and safety of LOXL2-specific AB0023 represents a new therapeutic approach with broad applicability in oncologic and fibrotic diseases.