This study is a fundamental work performed to obtain basic information about designing two-phase closed thermosyphons with a working fluid of FC-72 (C6F14). FC-72 is a kind of alternative refrigerant designed to be chemically safe and more environmentally friendly than any other conventional CFC refrigerants. To obtain experimental data on operational performances of a FC-72 two-phase closed thermosyphon, an experimental model was designed and manufactured with a micro fin groove copper tube with an outside diameter of 22.2 mm for its container, on which a series of operational performance tests were conducted. Its maximum capacity of heat transport rate was designed to be about 300-400 W. The focus was given to investigate the effects of such parameters as micro fin grooves and fill charge ratios on operational performances of the FC-72 two-phase closed thermosyphon. The experimental data on phase change heat transfer coefficients and heat transport limitations were compared with some corresponding correlations, and a couple of measures that would help to predict operational performances were suggested with some physical explanations.