By the use of a laboratory drilling equipment, the drilling rates of 33/4in tri-cone bits (3S, 3M and 3H type) were recorded at atmospheric pressure using water as circulating medium. For this test 17 kinds of rock were used, and compressive strength of these rocks was ranged from 200 to 3700kg/cm². Other physical properties of the rocks such as density, porosity, radial compressive strength, sound velocity, Young's modulus, Poisson's ratio, and Shore's hardness were measured. Drilling rate of the bits was directly affected by the compressive strength of a rock. Results of the measurement showed that the cone bits of this ordinal type were not effective for drilling hard rock with compressive strength of more than 2500kg/cm². Density of rock was possible to determine a proper bit weight. Shore's hardness was also used to some extent to assume a proper bit weight. In this study of limitted conditions there were no special relationships between the drilling rate and the radial compressive strength, sound velocity, Young's modulus, or Poisson's ratio.