Dynamic mechanical analysis (DMA) has been used extensively to characterize polymeric materials. This thesis investigates the use of this technique to characterize composite materials. Four material systems, all having the same fiber and the same matrix material, were systematically altered with different interphase regions. Initial run data indicates that the variation in fiber sizings create different interphase regions that are detectable by DMA. However, some post-cured specimens revealed that those differences are reduced with further heat treatment. Fiber sizing variation also affects the material response to thermal and mechanical cycling. Different fiber surface treatments have little effect on the dynamic mechanical response of the materials. It is shown that DMA is a test method that yields repeatable results and is capable of detecting small changes in composite constituents. / Master of Science