This paper presents results of ground-experimental study on the start-up characteristics of a Loop Heat Pipe. The physical process of start-up is described, and the explanation that "Pressure Transfer" leads to the saturated temperature rise in compensation chamber during start-up is first discussed. Start-up behaviors as a function of various parameters including vapor/liquid distribution in the evaporator, adverse elevation, start-up heat load, sink temperature are described and explained. A peculiar start-up phenomenon composed of two start-up scenarios was first observed at adverse elevations and is described.