The production and use of ordinary Portland cement in concrete have a significant effect on the surrounding environment by generating a large quantity of carbon dioxide and depleting the natural resource. The objective of this research is to partially replace ordinary Portland cement in concrete mixture with fly ash, which is a by-product from thermal power plant. The effect of fly ash content on compressive strength development of concrete is investigated. Three mixtures were designed with 10%, 20%, and 30% fly ash replacement for cement compared with a control mixture. Test results indicate that the workability of fresh concrete increases and the unit weight of concrete reduces with increasing fly ash content. The compressive strength of concrete with 10% fly ash is the highest, while that of concrete with 30% fly ash is the worst. Concrete with 20% fly ash has lower compressive strength than control concrete before 28 days; after 56 days it gets higher.