In this thesis the viscoelastic behavior of a composite with Unidirectional carbon fiber reinforcement (TORAYCA T700SC) and a vinyl ester (Derakane 8090) matrix is investigated. After having determined the resins viscoelastic properties by means of creep testing, the properties of the fiber bundle impregnated with resin are calculated using a micro mechanical model for a UD composite. Once the viscoelastic properties for both the resin and the reinforcement bundles are obtained, the viscoelastic response of a Non Crimp Fabric composite may be simulated in a macroscopic model by means of a finite element model. In this way it is possible to obtain the properties of a composite with arbitrary orientation and mixing relation between fiber and resin. These results can be modified to predict properties of other fiber reinforcements and resins. After a creep test of the matrix, followed by determination of the formation of fibre in the composite, one can use this work to retrieve the properties of the new material.