Direct numerical simulations of turbulent boundary layers over three-dimensional cubic roughness arrays were performed to investigate the effects of the spanwise spacing on turbulent characteristics. The staggered cube arrays were arranged periodically on the streamwise direction with varying p<SUB>s</SUB>/k at fixed p<SUB>x</SUB>/k. The wall-friction parameters have the maximum contribution at p<SUB>x</SUB>/k=3. The outer peak of the Reynolds stresses are increased with increasing p<SUB>x</SUB>/k which indicates the wall similarity is not satisfied with all cases. The size of the low-momentum regions over the rough walls is larger than the smooth wall, and the vortical structures grow to the outer layer. The vortical structures start to develop at the edges of the cubes. As p<SUB>x</SUB>/k increases the roughness array becomes sparse and the vortical structures grow to the outer region because other near vortical structures do not disturb to each other.