The thermal expansion behavior of unidirectional and balanced symmetrical unidirectional‐angle ply laminated boron and graphite fiber reinforced epoxy resin matrix composites is studied. The expansion coefficient is determined as a function of fiber orientation for a high modulus graphite/epoxy system, a high strength graphite/epoxy system, and a boron/epoxy system. Results for unidirectional materials, axial and transverse, are compared with strain compatability predictions. Effects of moisture absorption and evolution are discussed.