The low-energy structures of the mirror nuclei Ne21 and radioactive Na21 have been examined by using Coulomb excitation at the TRIUMF-ISAC radioactive ion beam facility. Beams of 5×106 ions/s were accelerated to 1.7 MeV/A and Coulomb excited in a 0.5 mg/cm2 natTi target. Scattered beam and target particles were detected by the segmented Si detector BAMBINO, while γ rays were observed by using two TIGRESS HPGe clover detectors perpendicular to the beam axis. For each isobar, Coulomb excitation from the 32+ ground state to the first excited 52+ state was observed and B(E2) values were determined by using the 2+→0+ de-excitation in Ti48 as a reference. The segmentation of BAMBINO was used to deduce tentative assignments for the signs of the mixing ratios between the E2 and M1 components of the transitions. The resulting B(E2) values are 131±9 e2 fm4 (25.4±1.7 W.u.) for Ne21 and 205±14 e2 fm4 (39.7±2.7 W.u.) for Na21. The fit to the present data and the known lifetimes determined E2/M1 mixing ratios and B(M1).