Clays show plastic behavior, strength decreases significantly at high water contents, and these clays may settle in high amounts. In order to build on these soils, the engineering properties of the soil must be developed. Engineering properties of clays can be improved by inclusion of chemical admixtures including cement, lime, fly ash, etc. In addition, the number of studies on the use of fibers in soil improvement has been increasing in recent years. In the study, the effects of basalt fiber and fly ash additives on the strength and permeability properties of problematic soils has been investigated. For this purpose, basalt fiber length (6-24 mm), basalt fiber percentage (0-1.5%), curing time (1-56 days) and percentage of fly ash (0-15%) were selected as variables. Experimental studies have been carried out using the L16 design table with 4 parameters and 4 levels specific to the Taguchi method. Unconfined compressive, splitting tensile and permeability tests were carried out on the samples prepared at optimum water content and maximum density values. As a result of statistical analysis, optimum parameters for unconfined compressive and splitting tensile tests; 18 mm basalt fiber length, 1% basalt fiber, 10% fly ash and 56 days curing time were obtained. The permeability coefficient increased with the increase in basalt fiber length and content. However, the permeability coefficient decreased with the increase in the percentage of fly ash.