ABSTRACT: Heterogeneous rock mass consisting of rock blocks that is surrounded by a weak matrix is regarded asblock-in-matrix-rocks (Bimrock). Obtaining samples from this type of rock mass according to the standardsand preparing them to be used in laboratory studies are often difficult. For this reason, it is quite difficultto determine the shear strength parameters and the mechanical properties such as uniaxial compressivestrength in these sorts of rocks. There are just a few laboratory studies over bimrocks, and there isn’t awidely accepted empirical approach in the field of rock mechanics available due to the limitations of theexisting empirical methods. In scope of this work, synthetic Bimrocks samples were prepared with differentgrain sizes and different volumetric grain ratio. Uniaxial compressive strength tests were conducted onprepared samples. As a result of the experiments, the effect of grain size and volumetric grain proportionon the strength of artificial Bimrock samples were investigated. Artificial Bimrock samples with 20%, 30%and 40% volumetric grain proportions were prepared in the laboratory using gravel shaving diameters0.6 to 9.5 mm. Plaster and water were used to form matrix. The uniaxial compressive strengths of the testsamples decrease from 0.68 MPa to 0.45 MPa as the grain size decreases; and increase from 0.51 MPa to0.66 MPa as the volumetric grain proportion increase. The results indicate that the uniaxial compressivestrength of Bimrocks increases with increasing grain size and volumetric grain proportion.