KSR-III, which launched successfully at December 2002 by KARI, was thrusted by liquid propulsion system. To assure static safety margin, four composite fins were assembled in the rear section. For weight reduction, fin structures were developed with composite sandwich materials. because high load was acted on compisite fins during flight, insurance of static and aeroelastic safety are main design concept. In this paper, flutter analysis model was verified by comparing modal ahalysis and modal test results. Modal analysis was performed using MSC/NASTRAN and modal test was performed using impact hammer and accelerometers. When comparing model shape and natrual frequency, test and analysis results matched very well and it confided analysis model of flutter analysis. In flutter analysis, subsonic and supersonic cases were studied by MSC/NASTRAN and transonic cases were studied by TSD(Transonic Small Disturbance) program. Also subsonic and supersonic case results were compared with that of MSC/NASTRAN.