Flutter experiments on six flexible slender body models like a spaceplane were conducted in a low speed wind tunnel. The model was supported vertically in its wing surface so as to be able to move freely in the horizontal plane. Theoretical analysis has been carried out by using Doublet-Point method for non-planer surfaces in calculation of unsteady aerodynamic force. The followings were revealed. 1) The so-called body flutter occurred in four modes with a rigid wing connected with its fuselage at one point different in its longitudinal position and the wing span and one model with a flexible wing connected at four points. 2) In another model with a flexible wing, a wing-fuselage coupled flutter occurred. 3) In all experiments the body divergence did not occur. 4) For the flutter-speed, -frequency and -mode, a resonable agreement is observed between experimental and theoretical results. 5) The theoretical analysis shows that the structural damping coefficient yields an influence on the flutter speed. 6) The flutter vibration in experiments was mild.