The interfacial structure of β–Si₃N₄ whisker reinforced 7075 aluminum alloy composite was examined using a high-resolution transmission electron microscope. As-cast and T6 materials have almost the same surface structures, and (100) facet of each whisker was considered to be covered with a continuous layer of M–Si–Al–O–N (M: Mg, Zn) with a lattice plane spacing of approximately 0.26 nm. This layer is considered to prevent the reaction between whiskers and aluminum. In contract, (110) whisker facets without such layers react in a different manner from (100) facets. A MgZn₂ phase or its solid solution containing aluminum was identified on the whisker surface of the as-cast material as a precipitate phase. Heat treatment was performed at temperatures of 823 K, 933 K, and 1073 K to confirm the reaction between whiskers and 7075 aluminum. With the formation of the liquid phase of 7075 aluminum, the reaction progressed rapidly and AlN particles were produced on the surfaces of the whiskers with the heat treatment at 1073 K.