Crystal structure, magnetization and specific-heat studies were performed on (U1−xLux)NiGa solid solutions in order to investigate effects of the U sublattice dilution by Lu on antiferromagnetism in UNiGa. In contrast to a number of transitions observed in UNiGa, the Lu substituted materials exhibit only one magnetic phase transition at which they order antiferromagnetically. Both the temperature of magnetic ordering and the estimated U magnetic moment decrease almost linearly with increasing x and vanish around x=0.3 which is accompanied by vanishing magnetic entropy. Simultaneously the critical field of metamagnetic transition increases but the transition obviously disappears for x>0.2. The rapid loss of magnetism with dilution of the U sublattice by nonmagnetic Lu is attributed to the band character of magnetic U 5f electrons.