A high positive spontaneous volume magnetostriction and a large high-field magnetic susceptibility accompanied by a considerable decrease of magnetic moment and Curie temperature under external pressure (with close values of dln(μU)/dp and dln(TC)/dp) have been observed in ferromagnetic β-UH3. All these characteristics lead to the conclusion of a prevailing itinerant character of the magnetism and a strong delocalization of the 5f electrons in this compound. This conclusion is also supported by a relatively low magnetic anisotropy and by a low anisotropic magnetostriction of β-UH3.