Precast hollow core slabs are mainly used in buildings as slab elements apart from their usage as bridge decks. Due to various structural or service requirements, openings are provided in these slabs. Provision of openings reduces the strength, stiffness and also change the failure modes of the hollow core slabs. Therefore, it is essential to strengthen the slabs so that the load deformation behaviour and failure mode does not change drastically. The objective of this study is to understand the behaviour of glass fibre reinforced polymer (GFRP) strengthened hollow core slabs with openings by external bonding technique. Ten full scale hollow core slabs with and without openings are tested to evaluate the effect of openings and effectiveness of GFRP strengthening. Shear span to depth ratio (a/d) and location of openings are considered as variables. It was observed that, provision of opening reduced the ultimate strength by about 43 % and GFRP strengthening of this slab restored strength to 87 % of the control specimen. Test results indicate that GFRP strengthening is an effective and cost viable technique for restoring the strength and stiffness of precast prestressed hollow core slabs due to openings. © 2016, RILEM.