Interactions between biological cells and surrounding extracellular matrix (ECM) materials modulate many cell behaviors including adhesion and migration. One key example of this cellmatrix reciprocity is in the context of angiogenesis, the sprouting of new blood vessels from preexisting vasculature. Vascular endothelial cells (VECs) create and remodel the ECM during this process. In vivo, the surrounding fluid environment includes high concentrations of macromolecules, and is considered “crowded” in comparison to in vitro environments. Here, we quantified the amount and organization of collagen IV, a prominent ECM component of VECs, that was produced by these cells over four weeks in vitro in the presence or absence of macromolecular crowder (MMC) nanoparticles that approximated in vivo crowding. In the presence of MMCs, the amount and degree of alignment of collagen IV was greater. This ECM difference emerged within one week and was sustained for over four weeks. We explored the effect of initial cell density (cells/µm2) on this matrix production, to consider potential differences at a wound site versus an intact vessel. Moreover, we found the biophysical effect of MMCs to be unmodulated by secretions from an adjacent cell type in microvessels (pericytes). These results suggest that macromolecular crowding plays a direct role in remodeling the basement membrane, and that such crowding can be induced in vitro to more closely approximate the cell microenvironment.