Often, there are a great need to introduce sectional openings in slabs as well as in wall structures for facility requirements. That opening can severely weaken the slabs due to the cut-out of both concrete and reinforcing steel. This research evaluates the effect of openings on the behaviour of reinforced concrete cantilever slabs. Six slabs including cut-out in addition to one slab without cut-out as a reference slab were tested up to failure under incremental monotonic loading. Size and location of openings are the main parameters that are investigated in this research. It can be conducted that the presence of openings in cantilever slabs showed a decrease in the flexural ultimate capacity and the stiffness of these slabs compared to the control slab without openings. It was also found that, the opening location had a pronounced effect on the overall structural performance of cantilever slabs