Shorttitle In this work a simultaneous determination of caffeine content was performed in sample of Sidama (Ethiopia) coffee, before and after roasting at either different temperature (140-2100c) or different exposure time (4-10min). A UV/VIS spectrophotometer method is used. A modest loss of caffeine was verified both in the roasting time and roasting temperature. Rate constant for chemical reactions at 2000 c were determined. The result shows weight loss increases during roasting. For pure caffeine molar decadic absorption coefficient and translational dipole moment were calculated.