The antinucleon-nuclei annihilation cross section $\sigma_{ann}$ at very low energy has been measured at the LEAR facility (CERN) during the 80's and 90's and recently at the Antiproton Decelerator. The antineutron data at momenta below 180 MeV/c on several nuclei showed a steep rise which is expected only for the antiproton projectile due to its negative charge. The difference between the antineutron and the antiproton interaction with nuclei can be investigated measuring the $\sigma_{ann}$ of the antiprotons on the same nuclei and at the same energies. So far a direct comparison of the $\sigma_{ann}$ is possible only for momenta below 80 MeV/c (on proton) and at 100 MeV/c (on Sn target). The ASACUSA collaboration recently performed an experiment to measure the $\sigma_{ann}$ of 100 MeV/c antiprotons on a carbon target whose preliminary results are presented here.