We investigated the mixing process of the Kenics type static mixer, in which the mixing is enhanced by both advective mixing and mixing due to molecular diffusion in order to propose an estimation method of the mixedness. The results show that the element divides, folds and stretches the mixing fluids and forms a lamellar structure with striation width la. The value of la decreases with an increase in the number of elements by la-(2^(n-1))^(-1), which represents the characteristics length of advective mixing. The characteristic length of mixing due to molecular diffusion ld can be estimated by solving the one-dimensional unsteady species conservation equation analytically. The macroscopic estimation and prediction method of mixedness is proposed as function of la and ld. When la>ld, the advective mixing is dominant, while, when la