Abstract: The viscoelastic behavior of glass microsphere reinforced rigid polyurethane syntactic foams(glass microsphere/RPUF) under different temperatures and humidities was investigated. The experimental results show that temperature and humidity have an obvious effect on viscoelastic behavior of glass microsphere/RPUF. With increasing the relative humidity, the loss factors value increases while the storage modulus decreases. Under the same temperature, the creep compliance increases as humidity increasing. Using the time-humidity super-position principle, each master curve can be shifted to collapse into the reference master curve by introducing shift factors for humidity, and the master curves of creep compliance at reference temperature(60 ℃) and humidity(50%RH) are put forward.