A fluorescent imaging agent composed of a folate receptor-alpha (FRa)-targeting ligand conjugated to a fluorescent near infrared (NIR) dye, that can be used for imaging of FRa-expressing tumor cells. Upon administration, the FRa-targeting moiety of OTL38 specifically binds to FRa expressed on tumor cells thus selectively delivering the fluorescent dye to FRa-expressing tumor cells. Upon NIR imaging, tumor cells fluoresce, which allows for the visualization and identification of FRa-overexpressing tumor cells. FRa, a high-affinity folate-binding protein and a member of the folate receptor family, is overexpressed in various cancer cell types.