A laboratory testing programme was carried out to investigate the influence of Locust Bean Waste Ash (LBWA) on cation exchange and plasticity characteristics of Ordinary Portland Cement (OPC) modified lateritic soil. Preliminary tests were carried out on the natural soil to determine its properties. Other tests were carried out on soil-cement mixtures with up to 4% OPC admixed with 8% locust bean waste ash content by dry weight. Improvement in the plasticity characteristics of the soil was reflected in the decrease of liquid limit, increase in plastic limit and decrease in plasticity index with increased cement and locust bean waste ash content. The results using analysis of variance showed statistical significance. These results showed that modification with cement and locust bean waste ash blend significantly improved the plasticity characteristics through cation exchange of the lateritic soil.