The Poisson's ratio of a solid under deformation is classically defined as the negative of the ratio between the lateral or transverse strain and the axial strain. Ideally for an elastic material, the Poisson's ratio is assumed to be a constant. However, for viscoelastic materials like polymers and polymer matrix composites this is also likely influenced by various factors like time [1], temperature, degree of cure and also on the strain. In this work, the evolution of the viscoelastic Poisson's ratio of the commercial LY5052 epoxy resin is studied under uniaxial tension subject to constant deformation stress relaxation testing. Measurements of the Poisson ratios are performed using contact extensometers and strain gages. Samples at five different cure states are manufactured and investigated. The relaxation testing is performed by loading the samples to 0.5% longitudinal strain and monitoring the relaxation behavior over a period of 24 hours per cure state. Poisson's ratio is observed to evolve from 0.32 to 0.44 over time depending on the cure state. Moreover the data indicates that the individual Poisson's ratio curves can be shifted horizontally following time-cure superposition. The shift functions used for this horizontal shifting are similar to those identified for DMTA tests for storage modulus under identical conditions. Following horizontal shifting, master curves that show the evolution of Poisson's ratio over time can be created for a particular reference cure state. This similarity of the shift functions in both micro-scale DMTA testing and macro-scale relaxation testing is an indicator of the validity of the shift factors. The observation is used to further develop a viscoelastic model which identifies the total shift function as the product of the temperature and cure shift functions.