A bulk acoustic wave (BAW) bacterial growth sensor has been proposed for study of inhibitory effects of tea by continuous monitoring of disturbances in Proteus growth in the aqueous extracts of various teas, e.g. green tea, Fuzhuan brick tea, Oolong tea, Kudin tea, and black tea. The kinetic parameters, e.g. asymptote (A), maximum specific growth rate (mu(m)), lag time (lambda), and generation time (g), accurately estimated by using the growth response model, have been first used to characterize antimicrobial properties of tea. All of the parameters were changed via the inhibitory effects by tea. Green tea gives the weakest inhibitory action while others show stronger inhibitory actions : These inhibitory effects have also been examined by using the pour plate count technique. Both of the results show that, in addition to the antimicrobial properties of tea polyphenols and catechins, etc., the inhibitory effects may be attributed to the metabolites produced during the fermentation processing of these teas except green tea. The conventional disk diffusion test has been used to determine the minimum inhibitory concentration (MIC) against P. rettgeri. The MICs of green tea, Fuzhuan brick tea, Oolong tea, and black tea were found to be 1113, 818.0, 681.2, and 510.4 mu g/mL, respectively. The BAW bacterial growth sensor has shown to have advantages over other techniques, including the disk diffusion test, photometry, and the impedance method.