The viscoelastic behavior was discussed for ideal suspensions consisting of spherical particles with hard-core potential between them. Unimodal ideal suspensions showed viscoelasticity with relaxation times proportional to the cube of the particulate radius. Bimodal ideal suspensions with a ratio of particulate radii below 4 had viscoelastic properties similar to those of unimodal ideal suspensions, of which the relaxation times were proportional to the product of the average particulate radius and the average of the particulate radius squared. However, bimodal ideal suspensions with a ratio greater than 5 showed two distinct relaxation modes. The fast relaxation mode was related to the motion of smaller particles and the slow relaxation mode was related to that of larger particles. The ratio of 5 should be a criterion whether or not the motion of two types of particles can be averaged into one set of modes with an average relaxation lime. Two models predicting frequency dependency of storage and loss moduli for bimodal ideal suspensions with the ratio of particle radii smaller than 4, the average radius model; and for those with greater than 5, the two-phase model, were proposed. Essential theological parameters such as zero shear and high-frequency-limiting viscosities were reasonably predicted by the models.