Discontinuities are known to have a significant impact on the engineering characteristics of the rock masses, governing their potential failure pattern, increasing their deformation, and reducing their strength. In particular, the impact of non-persistent joints on the strength and failure mechanism of rock mass needs to be investigated further. The impact of different flaw geometrical characteristics such as flaw inclination, flaw length, flaw aperture, and flaw filling on uniaxial compressive strength of specimens has not been investigated thoroughly. In this paper, a series of uniaxial compression tests were conducted on cylindrical specimens containing an open central flaw. The effect of different parameters such as flaw inclination, flaw length, flaw aperture, and filling on the uniaxial compressive strength of specimens have been investigated through laboratory experiments. Response Surface Methodology (RSM) is adopted to analyze the impact of flaw parameters on the compressive strength of the constructed samples. The results of the experiments show that flaw inclination and flaw length have a significant impact on the peak strength of the samples, meaning that strength increases by growing of flaw angle and decreases by increasing of flaw length. In addition, at a low flaw length, aperture affects the UCS significantly, while by increasing flaw length, its effect decreases dramatically, and strength drops at a flaw inclination of 45 degrees. Conversely, at a higher flaw length, by increasing flaw inclination, the UCS increases constantly. It also has been observed that changing the flaw aperture had no important effect on the peak strength.