Surface/ground water pollution caused by the inflow of acid water enriched with heavy metals poses a serious environmental problem around excavation sites where sulfide minerals chemically decompose. To establish a method to evaluate acid water drainage from rock, we examined the percolation and geochemical characteristics of rock. It became clear that it was possible to evaluate acid water drainage by using the following indices; (1) the pH value one hour after a batch-leaching test; (2) the rock's sulfur content; and (3) in the case of mudstone only, the S/Ca mole ratio of the rock.