Multi-stage satellite launch vehicles use interstage structures to connect two stages. The interstage structure carries huge axial compressive loads and is usually designed against buckling. Composite material-based interstage is the best alternative to metallic one, as use of composite materials leads to considerable reduction in weight and increase in payload gain. In this paper, efforts are made to design a honeycomb sandwich-based composite interstage with a margin of safety (MS) same as that of currently operational stringer stiffened interstage structure. Closed-form solutions for critical buckling load are used for preliminary design of the cylindrical sandwich structure, and geometrical parameters are arrived out. Moreover, this closed-form design buckling load has been validated using two separate finite element (FE) analysis methodology: (1) linear Eigenvalue buckling and (2) nonlinear structural analyses. After completing preliminary design and analysis of interstage, detailed design of interstage structure is carried out by incorporating the cut­outs in the sandwich cylinder similar to that of a typical interstage configuration. The incorporation of cutouts has resulted in lowering of buckling load warranting re-design of the interstage structure through an iterative non-linear FE structural analysis approach. The optimum size is arrived through the iterative procedure, such that the critical buckling load of the interstage structure is not changed significantly from the stringer stiffened configuration. The mass of the proposed composite interstage structure is found to be 158 kg lesser than the current metallic stringer stiffened interstage structure when the margin of safety is kept same. This will lead to substantial payload gain.