Experimental study to improve aerodynamic performances of RLV under the condition of constant fuselage volume has been conducted. Two means have been considered to maintain constant volume. One is stretching the fuselage and remaining fuselage-cross section configuration. Fuselage-cross section is an isosceles right triangle. The other is changing the fuselage-cross section configurations and remaining full length. 5-types Fuselage-cross sections are tested. The models are Wing-Body configuration, and have single delta wing modified NACA0010. The experiments have been conducted in a low speed wind tunnel. In experimental result, if fuselage is stretched, maximum lift coefficient CLmax and wing- stalled angle of attack are increased. This is related fuselage separation vortex. As fuselage is stretched, effected region by this vortex is expanded. So, vortex is more developed. Maximum lift-to-drag ratio (L/D)max is also increased. But too long fuselage, (L/D)max is not good. In case that fuselage-cross section is changed, same results are obtained. This cause is same. Flow visualization tells that separated region and location of formation of separation vortex are related to the differences.These results provided that stretching the fuselage moderately and selecting an isosceles right triangle or half circle fuselage-cross section configurations have been improved CLmax and (L/D)max.