A magnet assembly for a dental magnetic attachment comprising a cup-shaped yoke of substantially Ni-free ferritic stainless steel, a permanent magnet received in a recess of the cup-shaped yoke, a seal member sealing an opening of the cup-shaped yoke, and an abutment-welded portion of the seal member and the cup-shaped yoke; the seal member comprising a center portion of substantially Ni-free ferritic stainless steel; an intermediate portion of substantially Ni-free austenitic stainless steel having a nitrogen content of 0.5-2.0% by mass, and a peripheral portion made of substantially Ni-free ferritic stainless steel having a nitrogen content of 1.3% or less by mass, smaller than in the intermediate portion.