The influences of the molecular weight and chlorine content of chlorinated polyethylene (CPE) on the dynamic mechanical properties of an organic hybrid consisting of CPE and 3,9-bis [1,1-dimethyl-2{beta-(3-tert-butyl-4-hydroxy-5-methylphenyl)propiopyloxy}ethyl]-2,4,8,10-tetraoxaspiro [5,5]-undecane (AO-80) were investigated. All CPE/AO-80 hybrids clearly exhibited two kinds of relaxations, and their magnitudes varied according to the molecular weight and chlorine content of CPE. This was due to a change in the ratio of AO-80 molecules dispersed in the CPE-rich domain and the AO-80-rich domain. A comparison of the jump intensity in differential scanning calorimetry curves with the maximum value of the second tan delta peak demonstrated that the second relaxation was caused by the dissociation of intermolecular hydrogen bonding within the AO-80-rich domain.