The present invention is related to new peptide antagonists of alphavbeta3 receptor, designed on the basis of the crystal structure of integrin alphavbeta3 in complex with c(RGDf[NMe]V) and the NMR structure of echistatin. These peptides are potent and selective antagonists of the alphavbeta3 receptor and can be used as novel anticancer drugs and/or new class of diagnostic non-invasive tracers as suitable tools for alphavbeta3-targeted therapy and imaging.