AIM:: To investigate the effect of Chinese nutgall on experimental root caries remineralization. METHODS: The root caries with chemical demineralization model was prepared. The samples were treated with 30mg/ml Chinese nutgall, 20g/L NaF, 380g/L Ag(NH3)2F and deionized water respectively, then were soaked in the remineralization solution for 7d. The surface morphology, lesion depth and total volume of demineralization were observed through SEM and MRG. RESULTS: Before remineralization, through SEM, short blunt ecptoma was found on the surface of lesions of samples in Chinese nutgall group and Ag(NH3)2F group; while in NaF group, globular ecptoma was seen scattering on the surface of the lesions, together with lacune; in deionized group, there was Sharpey's fiber. After remineralization, the surface structure of samples in Chinese nutgall group and Ag(NH3)2F group became compacter and steadier, with presentation of small blotch and trabs; in NaF group, there was still lacune with trab- like structure on the surface of the samples; in deionized group, the surface of samples was honeycomb appearance. The analysis of each treatment through MRG showed that they had remarkable effect of enhancing remineralization on root caries, compared with deionized water (P<0.05). Among the treatments, Ag(NH_3)_2F showed the best effect, and there was no significant difference between Chinese nutgall group and NaF group.CONCLUSION: Chinese nutgall shows the effect of inhibiting the progress of experimental root caries and enhancing its remineralization .