Electrical resistivity and hardness measurements were conducted during isothermal aging treatments of an alumina particulate reinforced 6061 aluminum metal matrix composite and a monolithic 6061 aluminum control material. Transmission electron microscopy was utilized to examine the microstructural changes accompanying the changes in the resistivity of the monolithic during aging. In addition, differential scanning calorimetry was used to investigate the growth kinetics and thermal stability of the metastable phases in the control sample. From DSC experiments, the heats of formation of the metastable phases were determined as functions of aging time and temperature. These results were used to characterize the aging behavior of the matrix material. Keywords: Aluminum composite, Conductivity, Aluminum alloys. (jes)