Misalignment and unbalance is the most cause of machine vibration. An unbalanced rotor always cause more vibration and generates excessive force in the bearing area and reduces the life of the machine. Understanding and practicing the fundamentals of rotating shaft parameters is the first step in reducing unnecessary vibration, reducing maintenance costs and increasing machine uptime. In this paper, experimental studies were performed on a rotor dynamic test apparatus to predict the vibration spectrum for rotor unbalance. A self-designed simplified 3 pin type flexible coupling was used in the experiments. The rotor shaft accelerations were measured at four different speed using accelerometer and dual channel vibration analyzer (ADASH) under the balance (baseline) and unbalance conditions. The experimental and numerical (ANSYS) frequency spectra were also obtained for both base line and unbalanced condition under different unbalanced forces. The experimental predictions are in good agreement with the ANSYS results. Both the experimental and numerical (ANSYS) spectra show that unbalance can be characterized primarily by one times (1X) shaft running speed.