There are numerous negative social and environmental effects of overuse of river sand for construction. To reduce this, various substitutes have been used such as quarry dust, demolished concrete waste, industrial waste such as copper slag, eco sand etc. GBFS (Granulated Blast Furnace Slag) is a slag obtained from the manufacture of iron in steel industries. This research aims to investigate the possibility of replacing Granulated Blast Furnace Slag (GBFS) as sand substitutes in concrete. In this research, natural sand was replaced by GBFS in various percentages (0%, 25%, 50%, 75% and 100%) with a constant water cement ratio of 0.45. Tests such as sieve analysis, specific gravity, fineness modulus and bulk density were done for fine aggregates and GBFS sample. Different mixed proportions for different percentage replacement of fine aggregates was obtained for M30 grade concrete as per IS 10262: 2009. The durability test was done for cubes of control mix and GBFS mix (0%, 25%, 50%, 75% and 100%). It was found the strength of concrete was improved due to the addition of GBFS as fine aggregates. Test results showed that the compressive strength of concrete increased with increase in percentage of GBFS up to 75%. Beyond 75%, there was a marginal decrease in strength of concrete.