Random number sequences on the optimum design of steel castellated beams have an important effect in the minimum weight design. In the present research, this effect is investigated using an optimum design algorithm which is based on a recently developed improved harmony search method (IHS). Harmony search optimizer is a simulator of musically pleasing that is used to realize the experience of a musician for searching pleasing harmony, which is the musically performance process based numerical optimization technique. The minimum weights of both beams are taken as the objective functions while the design constraints are respectively implemented from The Steel Construction Institute Publication Numbers 5. The design methods adopted in these publications are consistent with BS5950 parts. The formulation of the design problem considering the limitations of the above mentioned turns out to be a discrete programming problem. The design algorithms based on the technique select the optimum Universal Beam sections, dimensional properties of hexagonal holes and total number of openings along the beam as design variables.