Objectives : The purpose of this study was to develop an experimental carious detector by which only carious-infected dentin is stained and to investigate bacterial invasion after removal of dentin based on staining using the experimental carious detector. Methodology : Micro Vickers Hardness (MVH) of the extracted human teeth was measured on the longitudinal section surface from the pulp chamber to the carious region using a micro hardness tester. The carious dentin was removed based on tactile sensitivity, and based on staining using conventional and experimental carious detectors. The MVH of the remaining dentin cavity wall was determined by observing the indentation beneath the cavity wall. The microstructure of the remaining dentin was observed using a SEM (5-4700, Hitachi, JAPAN) and the possibility of bacteria survival was examined using a Gram stained specimen. Results : The MVH of the remaining dentin cavity wall after removal of the carious dentin (25.5±7.8 : tactile sensitivity, 32.7±8.2 : experimental carious detector, 44.7±6.6 : conventional carious detector) was statistically significantly different by ANOVA with Fisher's PLSD (p<0.001). The dentin tubules of the cavity wall were completely closed with rod-like substances with a cubed structure after the carious dentin was removed using the experimental carious detector. In addition, no bacteria was observed in any of the specimens. Conclusion : It was possible to conclude that the carious-infected dentin was completely removed and sclerotic dentin was preserved under the guidance of the experimental carious detector stain composed of poly-propylene glycol and acid red.