Expansive soils, such as black cotton soils, are basically susceptible to detrimental volumetric changes, with changein moisture content. The cyclic wetting and drying process causes vertical movements in expansive soils and these movements lead to failure of structures. There have been many methods available to control expansiveness of these soils. The removal of expansive soils and replacement with suitable material has been widely practiced all over the world where there is suitable material within economic distances. Stabilization is another alternative being used worldwide. This research was conducted to study the effect of adding textile industry waste ash(TIWA) to expansive soil which is used as subgrade material. Expansive soil samples were collected in one a test pit and modified by adding 0%, 10%, 20% 30%, and 40% of TIWA to soil sample.In other words, the industrial waste material of the textile factory was used as stabilizer material. The soil employed in the experimental studies was obtained from Bahir Dar town. The experimental works had been carried out to check the improvement in the index and strength properties of expansive soil treated with textile wastes ash in varying percentages. A cycle of tests such as liquid limit test, plastic limit test, plasticity index test, California bearing ratio test (CBR) test, specific gravity test, sieve analysis test, linear shrinkage, unconfined compressive strength and grain size test were carried out on black cotton soil samples with different percentages TIWA. From index property testscompiled, the geotechnical property of the soil was not improved andit remained highly plastic. The result from soaked CBR test and both 3 day and 7 day curing time showed that 30% was an optimum content. In addition,the un-soaked CBR result showed improvement with optimum value of 20%. Even though the index properties as well as the strength of the expansive soil show improvement with the addition of textile waste ash, the soil didn’t fulfill the requirement set in the ERA 2002 specifications. Hence, TIWA cannot serve to treat expansive soil.