The CCL2-CCR2 chemokine axis has an important role in cancer progression where it contributes to metastatic dissemination of several cancer types (e.g., colon, breast, prostate). Tumor cell-derived CCL2 was shown to promote the recruitment of CCR2(+)/Ly6C(hi) monocytes and to induce vascular permeability of CCR2(+) endothelial cells in the lungs. Here we describe a novel decoy protein consisting of a CCL2 mutant protein fused to human serum albumin (dnCCL2-HSA chimera) with enhanced binding affinity to glycosaminoglycans that was tested in vivo. The monocyte-mediated tumor cell transendothelial migration was strongly reduced upon unfused dnCCL2 mutant treatment in vitro. dnCCL2-HSA chimera had an extended serum half-life and thus a prolonged exposure in vivo compared with the dnCCL2 mutant. dnCCL2-HSA chimera bound to the lung vasculature but caused minimal alterations in the leukocyte recruitment to the lungs. However, dnCCL2-HSA chimera treatment strongly reduced both lung vascular permeability and tumor cell seeding. Metastasis of MC-38GFP, 3LL, and LLC1 cells was significantly attenuated upon dnCCL2-HSA chimera treatment. Tumor cell seeding to the lungs resulted in enhanced expression of a proteoglycan syndecan-4 by endothelial cells that correlated with accumulation of the dnCCL2-HSA chimera in the vicinity of tumor cells. These findings demonstrate that the CCL2-based decoy protein effectively binds to the activated endothelium in lungs and blocks tumor cell extravasation through inhibition of vascular permeability.