The effect of silicon addition to aluminum on the thermophysical properties of Al was experimentally investigated. Thermal diffusivity, heat capacity, density, and thermal expansion of sintered Al-Si samples with Si content ranging 0–8 wt% were measured. For U-Mo/Al dispersion fuel for research reactors, an addition of Si (up to 8 wt% Si) to the Al matrix has been adopted as a method to reduce the formation of interaction layer between the U-Mo and the Al. In this study, the Si-added Al matrix was simulated by using a powder metallurgical method, in which an Al powder and a Si powder were mixed and sintered. All measured properties decreased with the addition of Si. The effect was most pronounced in thermal diffusivity while the decreases in heat capacity and density were relatively insignificant. The measured thermal conductivity from the present study was higher than those measured data for alloy samples available in the literature to the differences in the fabrication method. All measured data including this study, however, were lower than the prediction by the Bruggeman model. It is because the model assumes an ideal heat-transfer conditions such as spherical particles, homogeneous particle distribution, perfect bonding between Al and Si.