Fiber-filled thermosetting polymer composites are extensively used in aerospace industries. One disadvantage of these materials is cure induced or thermally induced residual stresses in the matrix, which may result in deteriorated performance and premature failure. This article explores the use of epoxy/multifunctional polyhedral oligomeric silsesquioxane (POSS) nanocomposites as resins with reduced thermal stress coefficients that result in mitigated residual stresses. The effect of POSS loading on the thermal stress coefficient of the epoxy/POSS nanocomposite resins was investigated from below the beta-relaxation to the alpha-relaxation, or glass transition temperature, (i.e., from -100 to 180 degrees C) by measuring the shear modulus and linear thermal expansion coefficient. The thermal stress coefficient of the epoxy/POSS nanocomposites is found to be a strong function of temperature, decreasing rapidly with decreasing temperature through the alpha-relaxation region, increasing in the vicinity of the beta-relaxation, and then decreasing below the temperature associated with the peak in the beta-relaxation. With increasing POSS content, the thermal stress coefficient is reduced compared with the neat resin in the vicinity of the alpha-relaxation; however, the thermal stress coefficient increases with increasing POSS content below the temperature of the beta-relaxation peak. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2719-2732, 2008