Abstract: The rheological behavior of the Bacillus thuringiensis fermentation broth and its microfiltration concentrated broths was studied at 30℃ and rotational speed ranging from 75 to 750 r/min. As the results confirmed, they were pseudoplastic fluid, the apparent viscosities decreased with the increase of shear rate and the pseudoplasticity increased with the increment of concentration. As to the concentrated broths, the apparent viscosities decreased with the increase of temperature or reduction of concentration, and the effect of temperature on their apparent viscosities was further described by Arrhenuis model. The activation energy(Ea) had no obvious variation in different concentrations and the effect of concentration on apparent viscosity was more noticeable than that of temperature. Moreover a model for describing the combined effects of temperature and concentration on the apparent viscosity was given, which could be used to predict apparent viscosity of the concentrated broth of Bacillus thuringiensis at different temperatures and concentrations in the process of microfiltration.