OBJECTIVE To evaluate the effect of compounds of Galla chinensis on the remineralisation of initial enamel carious lesions in vitro. METHODS Sixty bovine enamel blocks with early lesions were prepared and randomly divided into six treatment groups. The lesions were subjected to a pH-cycling regime for 12 days. Each daily cycle included 4x1min applications with one of six treatments; 1000ppm F aq. (as NaF, positive control); deionized water (negative control); or 4000ppm aqueous solutions of four G. chinensis extracts (GCEs); GCE, GCE-B, GCE-B1, or GCE-B2. Surface enamel microhardness was measured on the enamel blocks before and after demineralisation, and after pH-cycling, and percentage surface microhardness recovery (%SMHR) was calculated. The enamel specimens were then sectioned (thickness ca. 80microm) and examined by polarized light microscopy. RESULTS All samples rehardened significantly compared to baseline. Fluoride had a significantly greater effect than all other treatments. In the GCEs groups, %SMHR was significantly greater than DDW for the GCE, GCE-B and GCE-B1 groups. There was no significant difference between the GCE-B2 group and DDW. Polarized light microscopy showed that the thickness of the surface layer increased obviously in all specimens including NaF group, GCE group, GCE-B group and GCE-B1 group. Negative birefringent band appeared in the lesions body and the depth of the lesions was obviously reduced. CONCLUSIONS The present study has demonstrated the potential of three GCEs (GCE, GCE-B and GCE-B1) to effect net rehardening of artificial carious lesions under dynamic pH-cyclic conditions.