Cement paste is a suspension of cement particles in water. In this manuscript, a new theological equation is presented to simulate thixotropic behavior of cement paste. This new material model is based on the previous work done by Hattori and Izumi. More precisely, the coagulation rate and dispersion rate of the cement particles are assumed to play the dominating role in generating thixotropic behavior. This is a so-called microstructural approach. The current work introduces ' memory ' into the relevant shear viscosity equation (i.e. into the apparent viscosity). Two types of memory functions are used. One is the memory of recent coagulation rate and the other is of recent shear rate. Model evaluation is carried out by comparing experimental data with model prediction. The experimental data is obtained using the ConTec Viscometer 4. The model prediction is calculated with the software Viscometric-ViscoPlastic-Flow. (c) 2005 Elsevier B.V. All rights reserved.