Optical gain characteristics of InGaN/GaN double quantum well (QW) structures with embedded AlGaN δ layer are investigated using the multiband effective mass theory. These results are compared with those of single QW structure without a δ layer. The theoretical energies show very good agreement with the experimental results for both single and double QW structures. The inclusion effect of a δ layer is found to be dominant at a relatively low carrier density. A double QW structure has larger optical gain than the single QW structure, in particular, at higher carrier density.