Cement Kiln Dust (CKD) is a by-product generated throughout the production of Ordinary Portland Cement (OPC). It is normally emitted to the atmosphere or converted into liquid and subsequently drained out as effluents to landfills and wastage areas. It impacted human health and the environment negatively. However, it can be utilized in concrete as raw cement replacement materials due to its engineering properties which work as an alternative binder of OPC in addition to that it has benefits in creating economic and environmental advantages. This study aimed to modify CKD and investigate the chemical composition of normal-CKD and modified -CKD accordingly. The term modified noted that CKD has gone through a process of modification using heating process. The reactivity property of CKD was investigated using pH analysis. Then, mix proportions of different percentage of normal-CKD and modified -CKD were developed to study the addition effects on the compressive and flexural strength for different curing period. The trend of strength development over the addition of CKD was also analyzed. OPC was replaced by CKD at 0% and successively increased by 10% to 100% through binder weight (OPC). A fixed amount of water to binder (W/B) with a ratio of 0.45 was used for all hybrids. The mixes were formed into the specimen and tested for compressive strength and flexural strength at 7, 14 and 28 curing days. The medium particle size of CKD used was less than 10μm. The results of compressive and flexural strength showed that modified-CKD resulted in better properties and 10% replacement showed the maximum values of compressive and flexural strength as a result considered best percentage replacement in agreement with its noteworthy results.