Abstract: ⁹⁰Y-DTPA-Bz-NH-SA-c(KRGDf) and ⁹⁰Y-DTPA-Bz-NH-c(ERGDf) were prepared, and their in vitro and in vivo properties were compared. ITLC and HPLC show that the labeling yields of both compounds are more than 99% under the optimal conditions(pH=5.5, reacting at 80 ℃ for 20 min), and they are stable in vitro. The biodistribution in nude mice bearing human glioma xenografts reveals no significant difference between these two radiolabeled compounds on uptake for all of tissues at the experimental time points; and pretty good tumor targeting and in vivo stability; and two radiolabeled compounds are mainly excreted through kidneys, partly excreted through hepatobiliary system. The experimental data demonstrate that both of cyclic KRGDf and cyclic ERGDf are suitable for the further development of polymerconjugated RGD peptide drugs.