To compare the influence of cave air P CO 2 and drip rate on the drip water geochemistry, approximately one year of cave air monitoring and sampling of drip water were conducted at Inazumi Cave, Oita, northeastern Kyushu, Japan, from February to December 2014. The monitoring revealed that temperature dependent cave air ventilation controlled distinct seasonal variation in the cave air P CO 2 and minor variation in temperature and relative humidity with increasing distance from the cave entrance. In addition to traditional sampling of drip water, novel sampling methods were designed to compare the influence of the P CO 2 and the drip rate on the karstic and drip water geochemistry. The chemical analysis indicated that the karstic and drip water instantaneously outgassed CO 2 once in contact with low cave air P CO 2 . The drip rate alone, however, had less significant influence on the drip water geochemistry than the P CO 2 . The drip water P CO 2 was repeatedly lower than cave air P CO 2 , and this is probably due to prior calcite precipitation, to a temporal increase of the cave air P CO 2 by anthropogenic CO 2 , or to storage conditions of the sample; all of which cause alteration of drip water geochemistry from the original state.