Spent catalyst is a by-product generated by oil refineries. There are two types of spent catalysts produced from oil refineries in Oman; Zeolite catalyst generated at Sohar Refinery and Equilibrium catalyst generated at Mina Al-Fahl Refinery. Spent catalyst can be used in concrete applications due to its pozzolanic nature. This study investigates the potential use of spent catalysts in concrete as partial substitute of sand at w/c ratios of 0.5 and 0.7. Concrete mixtures with different proportions of spent catalyst (up to 25% as sand repalcement) were prepared. Concrete mixtures were evaluated for compressive strength, setting time, water absorption, and corrosion resistance. The results showed that using 25% of the Sohar refinery's spent catalyst as sand replacement gave 73% increase in the cubes compressive strength at w/c ratio of 0.7. However, using spent catalyst from Mina Al-Fahl Refinery as sand replacement decreases the compressive strength gradually with the increase of spent catalyst percentage. The results also indicated that the elapsed time decreased as the quantity of spent catalyst from both refineries increases. Negligible increase in the total water absorption was observed in concrete when both spent catalysts were used. Concrete specimens made with spent catalyst from Sohar Refinery showed good corrosion resistance than the control mixture whereas spent catalyst from Mina Al- Fahl Refinery accelerated the corrosion process.