Objective: The antibacterial effect of various R. coptidis were evaluated by microcalorimetry together with statistical analysis. Materials and methods: The dried roots of Coptis chinensis Franch, Coptis deltoidea C.Y. Cheng et Hsiao, and Coptis teeta Wall (Ranunculaceae) were identified by Prof. Xiao-He Xiao. The herbs were tested using thermal activity monitor (TAM) air isothermal microcalorimeter, ampoule mode, to evaluate the biological activity. The dynamic energy metabolism information about the Staphylococcus aureus growth at 37 degrees A degrees C was analyzed with principal component analysis. Results: From the principle component analysis on quantitative parameters, the action of various R. coptidis on S. aureus growth at 37 degrees A degrees C could be easily evaluated by analyzing the change of values of the two main parameters: the growth rate constant of first stage (k(1)) and the maximum heat rating of the first stage (P(1)). And the results of paired t-test show that there were no notable differences between inhibitory ratios calculated with k(1) and that of P(1). Using microdilution method, the minimal inhibitory concentrations (MIC) of C. chinensis, C. deltoidea, and C. teeta were detected, and they were 77.8 +/-+/- 2, 116.6 +/-+/- 4, 93.3 +/-+/- 2 mu mu g/mL, respectively. Discussion and conclusion: This work provided a useful method for the evaluation of antibacterial activity of various R. coptidis.