Microcrystalline powders of yttrium barium copper oxide [YBa2Cu3O7] have been prepared by conventional ceramic preparation technique. The powder belong to orthorhombic symmetry with unit cell dimensions 'a'=3.8214 angstrom, 'b'=3.8877 angstrom and 'c'=11.693 angstrom. XRD and SEM studies revealed that its particle size is in the micrometer range. Micro composites of polystyrene with different loading of yttrium barium copper oxide fillers were prepared by melt mixing in a brabender plasticorder at a rotor speed of 60 rpm. The lattice parameters of the constituent phases are the same in all the composites. Mechanical properties such as stress strain behavior, Young's modulus, and tensile strength were studied as a function of filler loading. Addition of filler enhances the Young's modulus of the polymer. Because of the poor filler-matrix adhesion, tensile strength and strain at break decreases with filler loading. To explore more carefully the degree of interfacial adhesion between the two phases, the results were analyzed by using models featuring an adhesion parameter. Finally experimental results were compared with theoretical predictions. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 1027-1041, 2010