OBJECTIVE To explore the feasibility of using laser fluorescence device for assessing caries removal in primary teeth in vitro. METHODS 8 primary molars with approximal caries were collected, and caries were removed in vitro. The laser fluorescence readings of dentin before and after caries removal were recorded. To judge the degree of caries removal by caries detector, polarizing microscope and dental microhardness tester. The correlation of DIAGNO-dent reading with Viker's Hardness was analyzed. The feasibility of using laser fluorescence for assessing caries removal was explored. RESULTS The average Viker's Hardness of dentin after caries removal with staining was (46.99 +/- 12.44) HV, and the average Viker's Hardness of normal control was (67.39 +/- 16.59) HV. There was significant difference between the two groups (P < 0.05). There was no significant difference between laser fluorescence readings before and after caries removal with staining (P > 0.05). And there was significant difference between the laser fluorescence readings before and after the caries removal without staining (P < 0.05). It was observed by polarizing microscope that there was no caries residue in sample, no matter stain or not. CONCLUSION The laser fluorescence could not distinguish stained dentin from caries, and is not suitable for assessing caries removal.