In this paper, the Flutter analysis of an aircraft wing carrying, elastically, an external store is studied. The wing is considered as a uniform cantilever beam and the external mass is connected to the wing by one spring and damper. The aeroelastic partial governing equations are determined via Hamilton’s variational principle. Also, modified Peter's finite-state aerodynamic model is employed. The resulting partial differential equations are transformed into a set of ordinary differential equations through the assume mode method. Effects of different situations like the wing without external mass, the wing with a rigidly attached external mass, and the wing with an elastically attached external mass on the flutter speed and frequency are investigated. The numerical results for a wing are compared with published results and good agreement is observed. Then, Simulation results for the wing with an elastically attached external mass are presented to show the effects of the wing sweep angle, store mass and its location and the spring rigidity constant on the wing flutter. Results show that sliding the external mass toward the wing tip in spanwise direction and also toward the trailing edge in chordwise direction decreases the flutter speed. Furthermore, increasing the store mass and spring constant decreases the wing flutter speed. Results show that increasing the wing sweep angle, increases the flutter speed, in all situations.