Objective: To evaluate the practical value of near-infrared light transillumination (NILT, DIAGNOcam) on detection of incipient proximal caries in primary molars. Methods: In this study, 4-9-year-old children with suspicious proximal lesions in primary molars were recruited. The target teeth were examined with clinical examination, bitewing radiograph and DIAGNOcam. And the caries indexes were rated as 0 (no caries), 1 (caries reaching outer 1/2 enamel), 2 (caries reaching inner 1/2 ena-mel), and 3 (dentine caries). Those primary molars with at least one of the adjacent molars according with the criteria of invasive treatment, i.e. the teeth were diagnosed as caries reaching inner 1/2 enamel or dentine with at least two detection methods, were included. The target teeth with caries index ≥2 accepted the invasive treatment. And the caries status of the adjacent teeth was observed under direct vision and those teeth of caries index ≥2 would also accept the invasive treatment. The relationship of lesions to enamel-dentine junction (EDJ) were recorded and used as reference standard to compare the sensitivity, specificity and accuracy of those three methods in detecting the incipient proximal caries in primary molars. Results: In this study, 36 children with 104 suspicious proximal lesions in primary molars were recruited, of which 5 were diagnosed as no caries, 20 were diagnosed as superficial enamel caries, and 79 accepted invasive treatment, of which 22 were diagnosed as EDJ caries, and 57 as dentine caries. The sensitivity of clinical examination, bitewing radiograph, and DIAGNOcam were 68.69%, 81.82%, 78.79%, respectively. The specificity were 100.00%, 100.00%, 80.00%, and the accuracy were 75.96%, 85.65%, 78.85%, respectively. As for superficial enamel caries, the sensitivity of cli-nical examination was lowest, only 10%, while DIAGNOcam was 60%, higher than 40% of bitewing radiograph. As for EDJ caries, the sensitivity of bitewing radiograph was highest as 86.36%, followed by DIAGNOcam 72.73% and clinical examination 68.18%. As for dentine caries, the sensitivity of the three detection methods were higher than 85%, of which bitewing radiograph was the highest as 94.74%. Conclusion: The accuracy of DIAGNOcam in detecting incipient proximal caries in primary molars was comparable to that of bitewing radiograph. It was safe, and convenient with no exposure to radiation, which was applicable to be used in pediatric dentistry.