The viscoelastic properties of Escherichia coli culture suspensions of various cell concentrations were studied in terms of relation to shear strain amplitude and angular frequency dependence. Samples of the suspensions were prepared by resuspension of a concentrated suspension obtained by centrifugation. Dynamic viscoelasticity for all cell concentrations at an angular frequency of omega=0.1 rad.s(-1) exhibited linear behavior up to a shear strain amplitude of about 0.02. The storage modulus decreased with am increase in shear strain amplitude above 0.02, while dynamic viscosity was not so noticeably influenced, Further, for samples of very high cell concentrations in particular, the dynamic viscosity increased with increasing shear strain amplitude, in parallel with the decrease in storage modulus. The angular frequency dependence of the storage modulus for samples of high cell concentrations was very low, since the. network of the suspension behaved as a relaxation mechanism having a long relaxation time. Masked dependence of viscoelasticity on cell concentration was observed, and considered to be caused by the development of a network structure composed of microbial floccules interacting with one another.