This study reports the achievement of ultrahigh electromechanical response in sodium niobate (NNO) thin films through the coexistence of antiferroelectric (AFE) and ferroelectric (FE) phases. By inducing structural instability from competing AFE and FE orders, the researchers achieved an effective piezoelectric coefficient (d₃₃,f*) of over 5,000 pm/V. The NNO thin films were grown on SrTiO₃ (STO) substrates with a (111) orientation, enabling the coexistence of AFE and FE phases. The AFE and FE phases exhibit a complex phase diagram with seven crystalline phases, including paraelectric (PE), AFE, and FE phases. The coexistence of these phases allows for a high degree of flexibility in polarization orientations, contributing to the enhanced piezoelectric response. The study also demonstrates the AFE–FE phase transition under an applied electric field, which leads to large strain and high piezoelectric coefficients. The electromechanical response was measured using a laser Doppler vibrometer, revealing a significant strain response under an applied electric field. The results show that the coexistence of AFE and FE phases in NNO thin films enables ultrahigh electromechanical performance, offering a new strategy for designing and exploiting antiferroelectric materials in electromechanical devices. The study highlights the importance of structural instability in enhancing electromechanical response and provides a general approach for designing such materials.This study reports the achievement of ultrahigh electromechanical response in sodium niobate (NNO) thin films through the coexistence of antiferroelectric (AFE) and ferroelectric (FE) phases. By inducing structural instability from competing AFE and FE orders, the researchers achieved an effective piezoelectric coefficient (d₃₃,f*) of over 5,000 pm/V. The NNO thin films were grown on SrTiO₃ (STO) substrates with a (111) orientation, enabling the coexistence of AFE and FE phases. The AFE and FE phases exhibit a complex phase diagram with seven crystalline phases, including paraelectric (PE), AFE, and FE phases. The coexistence of these phases allows for a high degree of flexibility in polarization orientations, contributing to the enhanced piezoelectric response. The study also demonstrates the AFE–FE phase transition under an applied electric field, which leads to large strain and high piezoelectric coefficients. The electromechanical response was measured using a laser Doppler vibrometer, revealing a significant strain response under an applied electric field. The results show that the coexistence of AFE and FE phases in NNO thin films enables ultrahigh electromechanical performance, offering a new strategy for designing and exploiting antiferroelectric materials in electromechanical devices. The study highlights the importance of structural instability in enhancing electromechanical response and provides a general approach for designing such materials.