In this paper, the aeroelastic modeling and conceptual flutter analysis of a simple 2-D box wing is investigated. For each wing the torsion and bending elasticity is simulated by two torsional and longitudinal springs at its elastic axis. Furthermore, the connection winglet is simulated by a longitudinal spring. The aeroelastic governing equations are derived using Lagrange’s equations. Also, for aeroelastic loads simulation on the box wing, the Theodorsen aerodynamic model is used. The effects of various design parameters such as front and rear wing physical and geometrical properties, the connection winglet angle and stiffness, and aircraft altitude on the flutter of the system are investigated. Results show that the connection winglet stiffness and angle have significant influence on the box wing flutter boundary.