Abstract： Objective To investigate the effect of different concentrations of sucrose on the bacteria composition and pH of in vitro biofilm derived from dental plaque.Methods Dental plaques from five caries-active people( DMFS ＞ 3 ) were mixed and cultivated in vitro under different sucrose concentrations (0,1.5,3.0,5.0,20.0 g/L) to form biofilm,from which DNAs of bacteria were extracted and further analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE).The pH was measured and bacteria counted in the biofilm.Results As the sucrose concentration increased,the number of bacteria species decreased.Higher sucrose concentration leaded to a lower minimum pH,which was 5.4 (0 g/L),4.7( 1.5 g/L),4.5(3.0 g/L),4.2(5.0 g/L),4.2(20.0 g/L),respectively.With sucrose in culture medium,the time needed for a minimum pH in the last 12 hours was much shorter( about 6 hours) than the time needed in the first 12 hours( 10 hours).The largest number of bacteria was observed at the sucrose concentration of 5.0 g/L.Conclusions The sucrose concentration may influnce the bacteria composition of biofilm derived from dental plaque and pH.Potential acidogenic and acid-tolerant bacterial community could be screened out in the culture medium with sucrose.