In this paper we report magnetic relaxation data for antiferromagnetic a-Fe2O3 particles of 5-nm mean diameter in the temperature range 0.1–25 K. The average spin value of these particles S.124 and the uniaxial anisotropy constant D.1.631022 K have been estimated from the experimental values of the blocking temperature and anisotropy field. The observed plateau in the magnetic viscosity from 3 K down to 100 mK agrees with the occurrence of spin tunneling from the ground state SZ5S. However, the scaling M vs T ln(n0t) is broken below 5 K, suggesting the occurrence of tunneling from excited states below this temperature.