The aim of this study is analyzing the acoustical quality of Bilkent University Amphitheater ODEON by means of assessing the fundamental acoustical parameters for both speech and music. Defining the problems, specifying the causes of the problems and providing a foundation for the ongoing suggestions are within the frame of the analysis. The parameters such as reverberation time, early decay time, clarity, definition, lateral fraction, sound pressure level and sound transmission index are calculated by the computer simulation technique for their assessment to be carried out. Initially, the results of the simulation software are compared with the previous real-size measurements of Bilkent ODEON for the unoccupied condition of the amphitheater, in order to ensure the accuracy of the software. Proving to be a valid tool, the software namely ODEON Room Acoustics Program, is used in the calculations for the occupied condition of the amphitheater as a basis of the study. The results are evaluated from the acoustical design standpoint of a multipurpose hall, which are followed by the suggestions for the improvement of the existing acoustical performance of the amphitheater. Finally, the suggestions are supported through the simulation results of the new hall that is acoustically renovated.