In order to keep the temperature of Light emitting diode (LED) lamp below some limitation, a finned plain-plate heat-pipe was presented and numerically investigated to predict heat transfer performance under natural convection. Two kinds of fin configurations were studied. It is found that 30° is the worst orientation for the fin configuration with the tops of every other two channels covered, while the worst orientation is around 60° for the fin configuration with channel tops opened. The thermal conductivity of fin material only has mild effect on the cooling capacity with 7 % difference when its thermal conductivity varies from 50 to 200 W/(m·k). The latter configuration has better thermal performance than the former at the same orientation, especially at relatively low inclined angle.