This study presents an entropy engineering strategy to achieve carrier-phonon decoupling in SrTiO₃-based perovskite thermoelectrics, significantly enhancing their thermoelectric figure of merit (zT). By introducing high entropy through solid solutions of Ba, Ca, and Pb at A sites, the lattice thermal conductivity was reduced to nearly the amorphous limit (1.25 W m⁻¹ K⁻¹), while the weighted mobility was improved to 65 cm² V⁻¹ s⁻¹. This decoupling led to a remarkable increase in μ_W/κ_L of -5.2 × 10³ cm³ K⁻¹ V⁻¹. The maximum zT of 0.24 at 488 K and an estimated zT of ~0.8 at 1173 K in (Sr₀.₂Ba₀.₂Ca₀.₂Pb₀.₂La₀.₂)TiO₃ films represent among the best results for n-type thermoelectric oxides. The entropy engineering strategy effectively decouples carrier-phonon transport by tuning A-site disorder, reducing lattice thermal conductivity, and modulating A-site radius and tolerance factor, thereby improving carrier mobility. The results demonstrate that entropy engineering is a promising approach to enhance zT in thermoelectrics by decoupling carrier-phonon transport. The study highlights the importance of entropy engineering in achieving high-performance thermoelectric materials through the rational design of A-site composition and structure.This study presents an entropy engineering strategy to achieve carrier-phonon decoupling in SrTiO₃-based perovskite thermoelectrics, significantly enhancing their thermoelectric figure of merit (zT). By introducing high entropy through solid solutions of Ba, Ca, and Pb at A sites, the lattice thermal conductivity was reduced to nearly the amorphous limit (1.25 W m⁻¹ K⁻¹), while the weighted mobility was improved to 65 cm² V⁻¹ s⁻¹. This decoupling led to a remarkable increase in μ_W/κ_L of -5.2 × 10³ cm³ K⁻¹ V⁻¹. The maximum zT of 0.24 at 488 K and an estimated zT of ~0.8 at 1173 K in (Sr₀.₂Ba₀.₂Ca₀.₂Pb₀.₂La₀.₂)TiO₃ films represent among the best results for n-type thermoelectric oxides. The entropy engineering strategy effectively decouples carrier-phonon transport by tuning A-site disorder, reducing lattice thermal conductivity, and modulating A-site radius and tolerance factor, thereby improving carrier mobility. The results demonstrate that entropy engineering is a promising approach to enhance zT in thermoelectrics by decoupling carrier-phonon transport. The study highlights the importance of entropy engineering in achieving high-performance thermoelectric materials through the rational design of A-site composition and structure.