Black cotton soil classified as an A-7-6 (24) soil on AASHTO classification collected from new Marte area of Borno state was modified with up to 4% cement and LBWA up to 8% by weight of the soil. The effect of locust bean waste ash (LBWA) on the cement modified soil was studied with respect to particle size distribution , Atterberg limits, compaction characteristics and shear strength parameters using three 3 compactive efforts namely, British Standard light (BSl), West African Standard (WAS), and British Standard heavy (BSh). Statistical analysis was then carried out on results obtained from the test conducted to determine the significant difference (i.e., p < 0.05) in the various soil - cement mixes using a two – way analysis of variance (ANOVA) with the Microsoft Excel Analysis Tool Pack Software. Analyses of the results of the soil-cement mixtures considered indicate increase in particle sizes, increase in the liquid limit and decrease in the plastic limit with corresponding increase in plasticity index, increase in maximum dry density (MDD) with increase in optimum moisture content (OMC) as well decrease in cohesion with increasing angle of internal friction all with higher locust bean waste ash content. The result also showed that the modified soil met the requirement of the Nigerian General Specification of not more tha

n 35% passing No. 200 sieve when used as a sub grade material in road construction. An optimal blend of 4% cement / 8% LBWA is recommended for the modification of black cotton soil.