Polymers and polymer-based materials are intensive implemented in many areas of engineering practice. These applications frequently have a very high performance demand, which makes their long-term characteristics of paramount importance. These materials were subject to degradation due to environmental factors, including light, temperature, stress, and others. Because of aging process, the physical and mechanical properties of these materials are significantly changed. This paper is devoted to the experimental investigations of this problem. The research program includes experiments on alternating of fatigue, creep, longterm climatic and deformation aging of polyurethane specimens. Results have shown the effect of considerable hardening and embrittlement during the aging process.