[en] Neutron diffraction and magnetic susceptibility measurements have been used to characterize the structural and magnetic properties of b-Pu₂O₃ with the hexagonal La₂O₃ structure. High-resolution neutron powder patterns combined with profile analysis have given the cell constants, atomic positional parameters, and the stoichiometry with high precision. The latter is in agreement with the value determined from thermodynamic methods. The antiferromagnetic structure in the temperature range 4 K< T< T/sub N/approx.19 K consists of Pu moments in the basal plane, but they vary along the c direction in a pseudospiral way. Two components are required to describe this modulation. The value of the maximum Pu moment at 10 K is approx.0.85 m/sub B/, each component having an amplitude of approx.0.6 m/sub B//Pu. At 4 K a spin rotation takes place so that mparallelc. Susceptibility measurements reflect the existence of T/sub N/ but show very little response near the spin rotation temperature