TEPC (Tissue Equivalent Proportional Counter) was usually used for high LET radiation dosimetry. We developed a prototype TEPC for micro-dosimetry in the range of $0.2{sim}300 keV/{mu}m$. And, the simulated site diameter of the TEPC is $2{mu}m$, of similar size to a cell nucleus. For purposes of characterization the response for high LET radiation of the TEPC has been investigated under 135MeV/u Carbon ions in HIMAC (Heavy Ion Medical Accelerator). We determined the gas multiplication factor and measured the lineal energy spectrum [yd(y)] of 135 MeV/u Carbon ions. The value of the gas multiplication factor was 315 at 700 V bias voltage. As a result of the experiment, we could more understand the performance of the TEPC for high LET (Linear Energy Transfer) radiation. And the procedure of high LET radiation dosimetry using TEPC is established.