The relations between suspension viscosity and parameters of representative particle size distributions, viz., log-normal, Rosin-Rammler (RR) and Gaudin-Schuhmann (GS) distributions, were derived from a flow characteristics model for continuous multimodal suspension that was developed based (in the model for discrete multimodal suspension (Ookawara and Ogawa, 2002). It was shown that, in the ease of log-normal distribution, the viscosity exponentially increases with geometric standard deviation, sigma(g), Since the viscosity is nearly constant in the sigma(g) range of below 1.1, the powder in this range can be regarded as monodisperse from the viewpoint of viscosity. It was also shown that, in both cases of RR and GS distributions, the viscosity rapidly decreases with index parameter n and approaches the viscosity of a unimodal suspension. This tendency is remarkable in the case of GS distribution because of its asymmetric characteristics.