This article introduces suspended anti-resonant acoustic waveguides (SARAWs) for enabling tunable Brillouin scattering on chip. Inspired by optical and acoustic anti-resonance principles, SARAWs offer superior acoustic mode confinement and high selectivity, supporting both forward and backward Brillouin scattering (SBS) on silicon-on-insulator (SOI) platforms. The structure simplifies design and fabrication, enabling breakthroughs in SBS performance. For forward SBS, a centimeter-scale SARAW achieves a net gain exceeding 6.4 dB. For backward SBS, an unprecedented Brillouin frequency shift of 27.6 GHz and a mechanical quality factor of 1960 are observed in silicon waveguides. SARAWs enhance photon-phonon coupling, enabling new opportunities in optomechanics, phononic circuits, and hybrid quantum systems. Brillouin scattering arises from photon-phonon coupling, with SBS finding applications in signal generation, processing, and devices like narrow linewidth lasers, microwave photonic filters, and distributed sensing. Integrated photonics has improved optical and acoustic mode confinement, advancing photon-phonon interactions. However, acoustic mode confinement remains challenging, with three main strategies: acoustic total internal reflection, acoustic impedance isolation, and phononic bandgaps. SARAWs overcome these limitations by using anti-resonant reflection, effectively confining acoustic modes and enabling flexible control of acoustic frequencies and modes. SARAWs are fabricated using a loading-effect etching technique, eliminating the need for overlay exposure and reducing inhomogeneous broadening. This method allows for high fabrication precision and simplifies waveguide design using genetic algorithms. SARAWs support both forward and backward SBS, achieving high Brillouin gain coefficients and mechanical quality factors. For forward SBS, a SARAW with a central waveguide width of 700 nm achieves a gain coefficient of 3530 W⁻¹m⁻¹, over 2000 times larger than standard single-mode fibers. For backward SBS, a SARAW with a central waveguide width of 1200 nm achieves an unprecedented mechanical quality factor of 1960 and a Brillouin frequency shift of 27.6 GHz. SARAWs demonstrate significant improvements in Brillouin net gain, with a threshold below 5 mW and a maximum net gain of 6.4 dB. They also enable high-quality backward SBS with a Brillouin gain coefficient of 600 W·m⁻¹ and a mechanical quality factor of 1300. SARAWs offer a low-loss, long-distance transmission platform for acoustic waves, with potential applications in phononic circuits and quantum systems. The study highlights the versatility and performance of SARAWs in integrated photon-phonon interactions, paving the way for future advancements in optomechanics and hybrid quantum systemsThis article introduces suspended anti-resonant acoustic waveguides (SARAWs) for enabling tunable Brillouin scattering on chip. Inspired by optical and acoustic anti-resonance principles, SARAWs offer superior acoustic mode confinement and high selectivity, supporting both forward and backward Brillouin scattering (SBS) on silicon-on-insulator (SOI) platforms. The structure simplifies design and fabrication, enabling breakthroughs in SBS performance. For forward SBS, a centimeter-scale SARAW achieves a net gain exceeding 6.4 dB. For backward SBS, an unprecedented Brillouin frequency shift of 27.6 GHz and a mechanical quality factor of 1960 are observed in silicon waveguides. SARAWs enhance photon-phonon coupling, enabling new opportunities in optomechanics, phononic circuits, and hybrid quantum systems. Brillouin scattering arises from photon-phonon coupling, with SBS finding applications in signal generation, processing, and devices like narrow linewidth lasers, microwave photonic filters, and distributed sensing. Integrated photonics has improved optical and acoustic mode confinement, advancing photon-phonon interactions. However, acoustic mode confinement remains challenging, with three main strategies: acoustic total internal reflection, acoustic impedance isolation, and phononic bandgaps. SARAWs overcome these limitations by using anti-resonant reflection, effectively confining acoustic modes and enabling flexible control of acoustic frequencies and modes. SARAWs are fabricated using a loading-effect etching technique, eliminating the need for overlay exposure and reducing inhomogeneous broadening. This method allows for high fabrication precision and simplifies waveguide design using genetic algorithms. SARAWs support both forward and backward SBS, achieving high Brillouin gain coefficients and mechanical quality factors. For forward SBS, a SARAW with a central waveguide width of 700 nm achieves a gain coefficient of 3530 W⁻¹m⁻¹, over 2000 times larger than standard single-mode fibers. For backward SBS, a SARAW with a central waveguide width of 1200 nm achieves an unprecedented mechanical quality factor of 1960 and a Brillouin frequency shift of 27.6 GHz. SARAWs demonstrate significant improvements in Brillouin net gain, with a threshold below 5 mW and a maximum net gain of 6.4 dB. They also enable high-quality backward SBS with a Brillouin gain coefficient of 600 W·m⁻¹ and a mechanical quality factor of 1300. SARAWs offer a low-loss, long-distance transmission platform for acoustic waves, with potential applications in phononic circuits and quantum systems. The study highlights the versatility and performance of SARAWs in integrated photon-phonon interactions, paving the way for future advancements in optomechanics and hybrid quantum systems