uPARAP (urokinase plasminogen activator receptor-associated protein) is a receptor for collagen and belongs to the macrophage mannose receptor family. uPARAP binding of collagens leads to collagen internalization and degradation and thus may contribute to matrix remodeling. Both collagens I and IV play an important role in lung development. To gain insight into the role of uPARAP-mediated collagen degradation during lung development, we studied the expression pattern of uPARAP by immunohistochemistry. Lungs were dissected from C57BL/6 mice from embryonic day 12.5 through postnatal day 14 and frozen in OCT. Five micrometer sections were obtained and immunohistochemistry was performed using polyclonal antibodies against uPARAP and collagen IV. uPARAP immmunoreactivity was detected in interstitial mesenchymal cells and airway smooth muscle cells at E 12.5, the earliest time point examined. uPARAP continued to be detected throughout lung development in interstitial cells and vascular and airway smooth muscle cells on postnatal days 2, 8, and 14. Increased immunoreactivity of uPARAP was seen with increasing developmental age, up to postnatal d.14. uPARAP co-localized with collagen IV primarily around airways and vasculature smooth muscle. We speculate that uPARAP-mediated collagen degradation plays a role in lung remodeling during embryonic and postnatal lung development.