This paper investigates the influence of molasses in reducing the plasticity of expansive clay soil. Plasticity tests of untreated soil and for soil treated with sugar cane molasses were carried out using standard procedures for testing soil for civil engineering purposes (BS1377:1990). Results showed that molasses reduced the plasticity index of the soil from an average of 39% for untreated soil to an average of 26% for treated soil at molasses content of 8% by weight of dry soil cured for 7 days. Observations of thin sections indicated that soil aggregations formed when 8% molasses content by weight of dry soil was added. However, the aggregations started to disintegrate when molasses content in the mixture exceeded 8%. This indicates that cane molasses reduced plasticity index through aggregation of soil particles and binding of the same by molasses. It was concluded that molasses could reduce the plasticity of expansive clay soil if molasses content in the soil did not exceed 8% by weight of dry soil.