Mechanical properties of polycyclo-olefins (PCOs) were investigated in the vicinity of the glass transition temperature (T.). According to tensile tests, the fracture modes of PCOs such as brittle, ductile, and impact processes. were largely dependent on the elongation speeds below T-g. In addition, the stress-strain curves were found to be superimposed by the shift factors on transverse and longitudinal axes, giving a typical master curve for tensile fracture behavior.