Rock is deformed and a failure zone based upon the ductility and brittleness of rocks occurs around the bit while drilling a blasthole. In order to better understand how the formation characteristics affect the drilling performance and the reason of the rock failure, a number of laboratory tests were conducted in this study. In this context, the effect of elastic and strength properties of rocks on the drilling properties was examined and also the influence of the brittleness and drillability on the mechanical properties was analyzed. The results have shown that the drilling rate index (DRI) agreed well with uniaxial compressive strength. This confirmed that the results of mechanical properties based on UCS have a high level of reliability while evaluating the drillability. Nevertheless, the results of DRI did not represent any correlation versus Young's modulus during blasthole drilling in rotary-percussive method although rotary drilling method indicated good relationships. Therefore, it is concluded that rock drilling properties do not account for a systematic relation to rock deformation in rotary-percussive drilling for medium-hard strength rocks while it does in rotary drilling method.