In this study, the crystal structure evolution of solid solutions between giant-tetragonal (GT) perovskite-type PbVO3 and BiCoO3, namely, (1 - x)PbVO3-xBiCoO3, is reported. The all-proportional solid solutions are successfully synthesized using a high-pressure and high-temperature method. A region of cubic phase is observed in the 0.4 ≤ x ≤ 0.75 range. The tetragonal distortion (c/a ratio) systematically decreases toward the cubic phase region, and these phases coexist in boundary regions. Magnetic susceptibility and soft X-ray absorption spectroscopy measurements reveal that 0.5PbVO3-0.5BiCoO3 possesses a valence state of V5+ and Co2+, which is different from the end members, V4+ and Co3+. The crystal structure changes stem from a self-doping effect induced by intermetallic charge transfer between the V and Co ions on the B-site (V4+ + Co3+ → V5+ + Co2+). This finding shows that tuning an electronic structure by making a solid solution is an effective way to control the stability of the GT structure.