Results of Pressure-Volume-Temperature measurement on Poly(methyl methacrylate) : Lead Titanate, PMMA : PbTiO3, composite system in the pressure and temperature range 0-200 MPa and 300-473 K, respectively, are presented. The thermal expansion coefficient in PMMA : PbTiO3 composite is expected to be quite complex because the polymer has positive thermal expansion coefficient, whereas the filler has a negative thermal expansion coefficient. In this present article, the effect of pressure on the volumetric thermal expansion coefficient in PMMA : PbTiO3 composite system is presented. It is shown that thermal expansion coefficient of the polymer can be tailored by adding filler which has negative thermal expansion coefficient. Theoretically, a simple additive rule is formulated which can predict the variation of expansion coefficient in the PMMA : PbTiO3 composite system. The limitation of the additive rule is also discussed. It is also shown that the glass transition temperature depends on filler concentration and also has strong pressure dependence. The reasons for large pressure dependence are discussed. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 2663-2667,2010