The objective of this study is to compare the viscoelastic material property of a vinyl ester (VE) resin using (1) the generalized 3-D viscoelastic constitutive equation with a Prony series representation and (2) a spectrum function model. The Prony series representation of the Generalized Kelvin model (GKM) is used to determine the Prony series coefficients through the linear least squares (LSQ) method. The Elastic-Viscoelastic Correspondence Principle (EVCP) and the Laplace transform are used in the spectrum function approach, which utilizes a carefully selected distribution function that has the potential to describe a wide range of materials. Short-term unidirectional tensile creep experiments are conducted at two stress levels and at four temperatures below the glass transition temperature of the VE polymer. Experimental strains in both the longitudinal and transverse directions and the applied stress are measured using the digital image correlation (DIC) technique. The measured data is subsequently used to determine the creep compliance function for each test configuration. The potential and limitations of each modeling approach are discussed.