Polymers and composites are usually exposed to influence of external factors (temperature, humidity, mechanical loading, etc.) which cause a time-dependent change of their structure and properties due to physical and chemical transformations. Thus, predicting mechanical and thermophysical properties of composite materials, it is necessary to consider results of research about structure and properties time-dependent variability of polymer resins under the influence of external factors. The aim of the work was to establish features of moisture absorption and to estimate influence of the absorbed moisture on mechanical and thermophysical properties of epoxy-based nanocomposites. Elastic characteristics of NC were experimentally investigated and described using Halpin-Tsai and Norris micromechanical models considering morphological features of filler particles. Viscoelastic behavior of epoxy resin and NC was analyzed after long-term moisture influence by means of linear integral equation of Boltzmann-Volterra considering a principle of moisture-time analogy. Application of thermomechanical analysis allowed establishing basic regularities for glass transition temperature for NC.