On a specific purpose to investigate and evaluate an important mechanical property of natural soil mixtures being shear response and frictional characteristics, an extensive laboratory experimental program has been conducted that consisted of a series of direct shear tests on various soil mixtures, including sand (S), silt (M) and clay (C), at different dry weight proportions [(i) S:100% – M:0% – C:0%; (ii) S:50% – M:50% – C:0%; (iii) S:50% – M:0% – C:50%; (iv) S:50% – M:25% – C:25%]. The experimental findings of the testing program have shown that the measured values of two crucial engineering design parameters such as the peak (τpeak) as well as the residual (τresidual) shear strengths for the soil mixtures are strongly influenced by the present soil type such that the detected values of τpeak, τresidual increase with an increase in sand content in the mixture whereas the attained values of τpeak, τresidual decrease with an increase in clay content in the mixture. Further, adding silt into sand-clay mixture improves strength characteristics such that the values of τpeak, τresidual become greater. On the other hand, adding silt into pure sand diminishes frictional resistance such that the values of τpeak, τresidual become lower. Consequently, it is seen that soil particle size (i.e. grain size) plays an important role on the shear strength behavior of the natural soil mixtures. Moreover, the displacement (δpeak) required to reach peak shear strength (τpeak) was also determined as a result of the direct shear tests. As such, the detected values of δpeak become larger with higher clay content available in the mixture, while the obtained values of δpeak become smaller with higher sand content existing in the mixture. Therefore, it is concluded that the higher the clay content, the mixture exhibits relatively more ductile shear behavior, whereas the higher the sand content, the mixture displays relatively more brittle shear response.