[en] A two-phase closed thermosyphon is a gravity assisted wick less heat pipe. The condenser section is located above the evaporator, so that condensate is returned by gravity. In this project a two-phase closed thermosyphon was designed and manufactured. An experimental investigation was performed in order to observe the effect of the inclination angel on the transport behaviour of a closed thermosyphon was performed in order to observe the effect of the inclination angle on the transport behavior of a closed two-phase thermosyphon. A vertical or inclined carbon steel pipe was used; this was electrically heated at the lower part (^heating Zone⁾ and it was cooled by air along the upper part (^heating Zone⁾. Between two areas there was the well insulated ^Transport Zone^. As working fluid water was used the heating zone was always flooded. The electric heat input and the inclination angle Φ toward the vertical position were varied in steps. The maximum heat flow rate in the tube proved t obe dependent upon the inclination. With a largest value of Qmaz=230w at 70-79 ^deg^. An effective thermal conductivity keff of the thermosyphon can be determined depending strongly on inclination and heat flow rate so the steeper the tube value the larger the heat flow rate the higher is the effective conductivity. The condensation in the cooling zone exhibits the largest transport resistance. The heat transfer with boiling in the heating zone shows large local differences which depends on inclination