The mechanical behavior of glassy PC was investigated as a function of strain and temperature by stress relaxation measurements and by dynamic mechanical measurements. For stress relaxation, the stress decay, measured by an Instron tensile tester, linearized vs logarithmic time from 1 sec to up to 16 h. From these data a plot of the relaxation time vs strain was obtained showing that the relaxation time decreased with increased strain. To separate the effect of the elastic and viscous components,E′andE″were investigated by the Rheovibron. At a constant strain level,E′showed a slight increase with time whileE″decreased considerably. With stepwise increase in strain,E′showed a slight decrease whileE″increased considerably. Furthermore, the dynamic mechanical spectra showed that the peak did not shift with strain, but intensified and broadened considerably. The stress relaxation can be related to the Rheovibron data.