The castellated beam is artificial from its parent solid I beam by cutting it in zigzag pattern and again amalgamation it by welding, so that the depth of the beam increases. Therefore, due to increase in depth of beam load carrying capacity of the parent I section is greater than before with same quantity of material. The increase in depth of castellated beam leads to web post buckling and lateral torsional buckling breakdown when these beams are subjected to loading. Generally the opening provided for castellated beams are hexagonal shaped openings, which are dispersed at regular intervals on the web portion of castellated beam. Castellated beams are comprehensively used as flexural members in steel construction. The inexpensive and structural advantages of these rudiments have prompted many researchers to investigate the failure performance of such structures. In this paper steel I section ISMB 150 is selected, castellated beams are fabricated with increase in thickness of stiffener and stiffener is provided between the two openings and beam is analyzed with the help of Finite Element Analysis (ABAQUS) software. Experimental testing is conceded out on beam with two points loading. The deflection at centre of beam and various failure patterns are studied. The prevalent use of castellated steel beam as a structural constituent has prompted several exploration in their structural behavior. The aim of this manuscript to find out increase or decrease the load carrying capacity of optimized stiffener is provided within the hexagonal opening of castellated beam. Study shows that use of stiffeners in the web portion of beam helps in minimizing these failures.