The aim of this paper is to find out an alternative way of stabilizing expansive soils. An expansive soil is a problematical soil type that causes for the disintegration of engineering structures built upon it. Research investigations consistently show that there are different methods and techniques employed to treat expansive soils. Yet, scientific inquiry in the field appears limited to North America, Western and Asian nations. There is a scarce of research on treatment of expansive soils within the Ethiopia context . Literature brought from North America, Western and Asian nations described various methods of treating expansive soil. Though, their costs are very high replacement method and chemical stabilizers are the most common one for treating expansive soil. With the escalated cost of construction these aforementioned pricey methods will not be practical to use. Based on the above premise an alternative solution to stabilize expansive soil with easy availability and parsimony is demanding. A number of foreign scientific Literatures revealed that cotton stalks ash an agricultural waste material used in the stabilization of expansive soil. Regarding the methods, to determine the expansiveness of the soil necessary laboratories tests that is index tests, strength tests, swelling tests were conducted. Following this, chemical compositions of cotton stalk ash were determined using Fluorescence X- ray diffraction method. The necessary laboratories tests that are index tests, strength tests and swelling tests are carried out to with varied percentages of cotton stalk ash ranging from 5% to 30% with a subsequent increment of 5%. The experimental analysis result shows that improvements in the geotechnical properties of expansive soil with varied percentage cotton stalk ash were obtained. Reaching 30% of cotton stalk ash satisfies the minimum requirement stated in the ERA manual. Utmost, the design and cost analysis of the cotton stack ash with replacement method were analyzed using statistical approach. Cotton stalk ashes were found to be cost effective, available and abundant method than replacement. Keywords: Expansive soil, Cotton stalk ash, Soil stabilization