Atomic hydrogen adsorptions on the (020) surface of α-Pu and the effects of surface relaxation on adsorption properties have been studied using a relativistic extension of the full-potential augmented plane wave with local orbital basis method. The surface has been modeled by a four-layer periodic slab consisting of 32 Pu atoms with a layer by layer anti-ferromagnetic arrangement. The adsorption properties for four different adsorption sites, namely the top, hollow, short bridge and long bridge sites have been investigated in detail. All computations have been carried out at two different theoretical levels, namely the scalar relativistic level without spin–orbit interaction (SR-NSO) and the fully relativistic level with spin–orbit interaction (FR-SO). The effect of relaxation has also been studied by calculating adsorption properties both on relaxed and non-relaxed Pu surfaces. Our studies show that the short bridge is the most favorable site for hydrogen adsorption with chemisorptions energies of 2.78 and 2.75 eV, respectively, at the two levels of theory. Neither spin–orbit coupling nor surface relaxation appears to have significant effects on adsorption.