The purpose of study was to measure the interrater reliability of the caries diagnostic instrument, Diagnodent(KaVo, Germany), using a new laser fluorescence technique. Occlusal surfaces and smooth surfaces of one hundred extracted human premolars and molars were examined by four dentists. Pearson correlation coeffcients were 0703 to 0.870 for occlusal surfaces and 0.764 to 0.932 for smooth surfaces (P<0.01, all). Reliability coefficients which were calculated by intraclass correlation coefficients were 0.9450 for occlusal surfaces and 0.9605 for smooth surfaces. Therefore, the interrater reliability of caries diagnosis by Diagnodent is very high, and the rater training would be necessary more for occlusal surfaces than for smooth surfaces.