A three-dimensional micromechanics-based analytical model is developed to investigate the influence of interphase on the thermo-mechanical properties of three-phase composites. The representative volume element (RVE) of composites is extended to c x r x h cells in three dimensions and the RVE consists of three phases including filler, matrix and interphase. The arrangement state of filler within the matrix materials is assumed to be random with uniform distribution. Fillers are surrounded by the interphase in the whole composite. The effects of interphase such as its thickness and stiffness on the thermo-mechanical properties of composite with various aspect ratios of filler are studied. The results illustrate that while the effects of interphase is significant for composites with randomly distributed spherical particles, it turns to be less effective as the aspect ratio of filler of composite increases. Moreover, the results demonstrate that the effect of interphase on the thermo-mechanical properties of fibrous composites in the transverse direction is more significant than that of fiber composites in the longitudinal direction.