Domain-wall orientations of antiferroelectric PbYb1/2Nb1/2O3 were analyzed by group symmetry and spontaneous strain methods. Both of the methods indicate similar results. PbYb1/2Nb1/2O3 has two types of domain-walls, i.e. W and W'-walls. The breaking of symmetry during ferroelastic transition occurs at (100), (010), (011), (0 (1) over bar 1), ((1) over bar 01) and (101) mirror planes of the cubic prototype. The W'-wall planes are approximately ((2) over bar 33)(m), (2 (3) over bar 3)(m), ((3) over bar 23)(m) and (3 (2) over bar 3)(m) at room temperature.