Kneading with a double-blade batch kneader mixer for wet particle systems combines both the convective and dispersive mixing processes. In this paper, we show that the mixing phenomena in the kneader can be analyzed by a mathematical model. Namely, for analysis of this mixing process, we derived an analytical equation considering both convective and dispersive mixing with the following three dimensionless numbers. The first dimensionless number represents the convective mixing of wet particle systems, which is the dimensionless interchange amount between two kneading vessels. The second dimensionless number represents dispersive mixing, which is advanced by compression and the rolling effect between the wall and the rotating blades. The last dimensionless number indicates the contribution of dispersive mixing to the total mixing. To determine each dimensionless number value, we also derived an empirical equation using only the rheological properties of the wet particle systems, namely, plastic viscosity, mu(0), and yield stress, tau(0). We ascertained that the analytical equation proposed in this study can estimate the mixing phenomena with high precision by verifying the estimated values with experimental results for various kinds of wet particle systems in a batch kneader with sigma blades.