In recent years, smart devices such as smartphones and tablets have become increasingly popular. The miniaturization, thinning, and faster processing speeds of these devices have raised concerns about controlling the temperature due to the increase in heat generation. High-performance cooling devices are required, but existing heat dissipation technologies are reaching their performance limits, and there is an urgent need to create new heat dissipation technologies. Therefore, loop heat pipes (LHPs) are attracting attention as a highly efficient heat transport technology. A LHP is a two-phase heat transfer device that uses latent heat of vaporization and is driven by capillary force. Therefore, a LHP can transport heat without power, and compared to other capillary-driven devices; the LHP can overcome the pressure loss better due to the location of the wick in the evaporator. In this study, a 0.3-mm-thick ultra-thin LHP was designed and fabricated, and its heat transfer characteristics were experimentally and analytically evaluated. First, a steady-state numerical model was developed specifically for the ultra-thin copper LHP, and the design was based on this model. The overall size of the LHP was designed to be mounted on a small and card-type device. To evaluate the LHP's heat transport performance, we measured the temperature of each component of the LHP in response to heat input. The LHP successfully demonstrated an effective thermal conductivity of approximately 12,300 W/m/K, which is 10 times higher than that of a high thermal conductivity graphite sheet.