In this paper, we report on terahertz spectral properties of polymer medical films cross-linked by electron beam irradiation. This is significant because it shows the potentials for novel technique to monitor of crosslinking state in polymer materials. We were able to clearly distinguished to cross-linked and noncross-linked medical films, which were manufactured with a PEO based synthetic polymer, in our conducted experiments. The THz-TDS method has potential as a useful nondestructive technique for polymer inspection and analysis.