Superconducting proximity junctions made of topological insulator (TI) nanoribbons (NRs) provide a useful platform for studying topological superconductivity. We report on the fabrication and measurement of Josephson junctions (JJs) using Sb-doped Bi2Se3 NRs in contact with Al electrodes. Aharonov–Bohm and Altshuler–Aronov–Spivak oscillations of the axial magneto-conductance of TI NR were observed, indicating the existence of metallic surface states along the circumference of the TI NR. We observed the supercurrent in the TI NR JJ and subharmonic gap structures of the differential conductance due to multiple Andreev reflections. The interface transparency of the TI NR JJs estimated based on the excess current reaches τ = 0.83, which is among the highest values reported for TI JJs. The temperature dependence of critical current is consistent with the short and ballistic junction model confirming the formation of highly transparent superconducting contacts on the TI NR. Our observations would be useful for exploring topological Josephson effects in TI NRs. Display omitted •Superconducting-proximity junctions were made of Sb-doped Bi2Se3 topological insulator (TI) nanoribbon (NR).•Our TI NR exhibited h/e- and h/2e-periodic magnetoconductance oscillations with the axial magnetic field.•We observed the subharmonic gap structures of the differential conductance due to the multiple Andreev reflections.•The interface transparency was estimated to be 0.83, which is among the highest values reported so far.