SrRuO3, a p-type metallic conductor with a small thermopower, and SrTiO3, a p-type insulator with a large thermopower in its hyperstoichiometric state, have been reported to make a complete solid solution. It is, thus, suggested that the thermoelectric power factor, conductivity times thermopower squared (σθ2), may be best optimized by mixing these two extreme oxides. In order to explore this possibility, we examined σ and θ of the solution Sr(Ru1-xTix)O3 against composition (0 ≤ x ≤ 1), temperature (300 ≤ T/K < 1000) and oxygen activity (-4≤logaO2<0), and subsequently its crystallographic structure against x at room temperature. It has been found that, contrary to literature, there falls a miscibility gap over the composition range 0.1 < x < 0.6. While there occurs a metal-to-insulator transition crossing the miscibility gap, θ remains little dependent on T and aO2 for the compositions up to x = 0.9. Unexpectedly, however, θ changes its sign twice with increasing x, indicating the majority carrier type changes from p to n at a composition in 0.6 < x < 0.9 and back to p at a composition in 0.9 < x < 1.0, whereas σ decreases monotonically. The highest power factor is observed, contrary to the expectation, at x = 0 (pure SrRuO3) on the order of 10-4 W/mK2. The origin of the repeated carrier-type changes is discussed in terms of electronic-structure change. © 2014 American Physical Society.