This in vitro study investigated the relationship between assessments of dentin caries using a laser fluorescence device (DIAGNOdent) and a caries detector dye during caries removal. The dentin of eight extracted carious molars was removed at 300-microm interval points from the dentin surface toward the pulp chamber. Before and after each removal, images of the carious surfaces were taken in association with color-matching stickers (for color correction) and the surfaces were evaluated by DIAGNOdent based on fluorescence emission from the tooth surface. For the L* values (CIE 1976 L*a*b* color system), there was a strong negative correlation between DIAGNOdent results and the corrected L* values of the carious surfaces (Pearson's correlation coefficient: -0.853); additionally, there was a significant correlation between them (p<0.05). However, there were no significant correlations between the DIAGNOdent results and the corrected a* and b* values of the carious surfaces (Pearson's correlation coefficients: 0.108 and 0.018 respectively). In conclusion, DIAGNOdent was shown to be applicable for caries diagnosis during caries removal.