Recently it has become common practice to cut multiple openings or large opening in the web of steel beams. This results in a considerable reduction of story height and saving in building costs. This paper is described to the ultimate strength and failure modes of the experimental work to the 23 beams, containing two rectangular openings with or without horizontal reinforcement. The results of the experiments are as follows; 1) In case the width of web-post is narrow below 1.0H, the ultimate strength is fallen. 2) Failure modes of beams with multiple openings are composed of multiple opening interaction failure(failure mode A), single opening failure(failure mode B), multiple opening failure(failure mode C) in conformity to interaction between openings. The minimum width of web-post in order to become failure mode B is wide above 1.0H.