<p>Honeycomb sandwich constructions with composite face sheets are extensively used in aerospace structures. The face sheets are generally made as a combination of unidirectional and bi-directional plies. The modulus of the face sheets plays an important role in the design of the structural component. They are determined from the modulus of the individual ply, applying the lamination theory. Modulus of the individual ply is determined through the testing of the laminates as per ASTM standards. In this work, it is shown experimentally that the modulus of unidirectional ply when it is a part of a face sheet in a honeycomb sandwich construction manufactured through co-curing process is significantly less compared to the value of modulus obtained from the tests on laminates. This is because the parameters involved in the co-curing process of manufacturing honeycomb sandwich panels are different from the parameters used in the manufacturing of the laminates. In the absence of this work, higher modulus than the actual will be used in the structural design of honeycomb sandwich type structure, resulting in large error in the predicted strain as well as the natural frequency of the fundamental lateral mode of spacecraft.</p>