The physical properties of sedimentary rocks in the coal fields were studied. Sandstones and shales are major samples among the core samples from Samchuck and Boeun coal fields. The measured properties were seismic velocities (P and S-wave), electrical resistivity, density and porosity. The relationships between physical properties were analyzed by using the cross plots. Summarized results are as follows : 1. Compressional wave velocity is approximately linearly related to shear wave velocity and the velocity ratio Vp/Vs of shales has slightly larger value than that of sandstone. And with increasing Vp, the velocity ratio Vp/Vs decreases because the effect of porosity and clay content on Vs is larger than on Vp. 2. In the case of sandstones, as porosity increases, P-wave velocity decreases slowly, but effect on the density is not apparent. In the case of shales, as porosity increases, both P-wave velocity and density decrease. 3. The values and variation range of density of sandstones are relatively small as compared to those of shales. But the range of elastic wave velocities of both rocks are appeared to be similar. 4. Seismic velocity is power-functionally related to electrical resistivity, and the value of the power is appeared to be larger for sandstones than for shales. 5. Because samples from Boeun field are slightly metamorphosed, the values of electrical resistivity are larger than those of samples from Samchuk field.