To gain the best performance of dielectric properties of polyurethane based carbonate, in the part we try to modify the structure and the hard segment of polyurethane to improved it dielectric constant and dielectric loss but the dielectric constant obtained is still low. The possible way to increase dielectric constant that will dramatically change in the dielectric value is by making a composite material. Barium strontium titanate (BST) is the lead-free ceramic that provides high dielectric and piezo constant, in addition, it is a non-toxic ceramic. Therefore, the new organic-inorganic composite was proposed. Polyurethane based carbonate that has a thermoset structure was selected to use as a matrix and Ba0.6Sr0.4TiO3 was selected to use as a filler to studies the influence of filler on physical properties and the improvement of dielectric properties in polyurethane. This organic-inorganic composite was synthesized using a prepolymer method by varies types of filler (surface modified filler and unmodified filler), and filler contents (20, 40, 60 phr or 0.048, 0.092, 0.140 Vf, of composite). The polymer film was made by solution casting. The result shows that as increase filler contents, it disturbed the crystalline formation of the matrix, the glass transition temperature of polyurethane base carbonate was increased, and the mechanical properties of the composites were dropped. The highest dielectric constant was found in the composite with filler content 60 phr (ɛ’ = 6.89, Tanδ = 0.064, at 103 Hz). The chemical modified filler was done by using hydrogen peroxide and 3-aminopropyl trimethoxysilane (APTES) as it was expected to improve the dielectric properties of the composite. The organic-inorganic composite with hydrogen peroxide and APTES modified surface of filler with filler content 20 phr has the highest dielectric constant (ɛ’ = 7.24, Tanδ = 0.062, at 103 Hz). The contribution of filler on dielectric properties was analyzed and the model of mixing was used