The dynamic mechanical behaviour of a series of hydrogenated syndiotactic polystyrenes (KsPS) with various degrees of hydrogenation has been investigated. In the case of crystallized HsPS samples, the primary dispersion is much broader due to the overlapping of two glass relaxation processes arising from one purely amorphous component and the other amorphous component under restraint by crystallites, as seen in semicrystalline polymers. There exist two secondary dispersions ascribed to chair-chair flip motion and oscillatory rotation of the cyclohexyl group in the range from 110 to 250 K. As compared with glassy complete HsPS, the strength of loss tangent (tan delta) peaks ascribed to the molecular motions of the cyclohexyl group in the crystalline polymer was lowered, suggesting that the molecular motions of this group in the crystalline part are sterically hindered.