Abstract We aimed to determine whether dye-enhanced quantitative light-induced fluorescence (DEQLF), wherein porous structure of caries lesions is stained with a fluorescent dye, could quantitatively distinguish between active and inactive caries. A total of 126 bovine specimens were prepared to artificially simulate caries activity. Active caries were demineralized with 1% carbopol solution for 3 (A 3 ), 5 (A 5 ), and 10 days (A 10 ). For inactive caries, half specimens in each group were remineralized with 2% NaF and reallocated into three groups (I 3 , I 5 , and I 10 , respectively). Wet specimens were dried with compressed air for 10 s and then dyed with 100-µM sodium fluorescein for 10 s. Fluorescence images of speicmens were captured with a QLF-digital 2 + Biluminator. Fluorescence intensity (ΔG) was measured in fluorescence images of dyed specimens. ΔG between active and inactive groups was compared using independent t -test, and ΔG among active groups (or inactive groups) were compared using ANOVA (α = 0.05). ΔG in the active groups was 33.7–59.0 higher than that in the inactive groups ( P  < 0.001). Except between I3 and I5, there was significant differences in ΔG according to the demineralization period ( P  < 0.001). DEQLF might be used to evaluate early caries activity, and longitudinally monitor changes in lesion activity.