Protein microspheres have been used in the fields of biomedical imaging and drug delivery, but surface modification for cell targeting has been problematic. We have for the first time used an electrostatic adhesion approach to adhere arginine-glutamic acid-aspartic acid (RGD) containing peptides to the surface of protein microspheres for the purpose of targeting these vesicles to tumor cells. RGD sequences are recognized by integrin membrane receptors, which are overexpressed in various tumors. We have succeeded in modifying the surface of serum albumin core-shell microspheres, which have a fluorescent nonaqueous core by using several polylysine peptides containing the RGD sequence. Fluorescence microscopy reveals that these modified microspheres are selectively bound and taken up by HT29 human colon cancer cells in vitro.