We report an observation of a 148-fold suppression of resonant absorption of keV photons from exp (-5.2) to exp(-0.2) with preservation of their spectral and temporal characteristics in an ensemble of the resonant two-level 57 Fe nuclei at room temperature. The transparency was induced via collective acoustic oscillations of nuclei. The proposed technique allows extending the concept of induced optical transparency to a hard x-ray/-ray range and paves the way for acoustically controllable interface between x-ray/-ray photons and nuclear ensembles, advancing the field of x-ray/-ray quantum optics.The induced transparency of opaque medium for resonant electromagnetic radiation is a powerful tool for manipulating the field-matter interaction. The study of phenomena associated with transparency induced in natural and artificial quantum and classical systems for resonant electromagnetic radiation in a wide spectral range from microwaves to γ-rays, as well as their applications, is an extremely broad area of research [1][2][3][4][5][6][7][8][9][10][11][12], extended also to acoustic waves [13,14]. Self-induced transparency [1], transparency via Autler-Townes splitting (ATS) [2,3], and electromagnetically induced transparency (EIT) [4,5] including their analogs in various quantum and classical systems [6][7][8][9][10][11], are just several examples of numerous techniques for suppression of resonant absorption. Important applications of induced optical transparency such as high refractive index and nonlinearities at the few-photon level, slow and stored light, optical quantum information processing, etc. stimulate a development of similar techniques in the hard x-ray/γ-ray domain. Highenergy 10˗100-keV photons can be easier detected and tighter focused than optical photons [15], while corresponding resonant recoilless nuclear transitions have orders of magnitude narrower linewidths at room temperature than optical atomic transitions at a comparable solid density [12,16]. These features are promising for realization of very compact and efficient interfaces between single hard x-ray/-ray photons and nuclear ensembles. However, the common tools for controlling quantum optical interfaces, such as intense spectrally narrow coherent sources and highfinesse cavities are still unavailable in hard x-ray/-ray range, preventing from a direct realization of the basic optical transparency techniques such as EIT and ATS-transparency, for high-energy photons. Several different techniques to control resonant interaction between hard x-ray/-ray photons and nuclear ensembles were developed, based on variation of hyperfine or external magnetic field [10,17,18], mechanical displacement (periodic or non-periodic) of an absorber or source with respect to each other including acoustic vibration [12,16,[19][20][21][22][23][24][25][26][27], and placing nuclei into a spatial sandwich-like nano-structure [11]. The 25% reduction in absorption of 14.4-keV photons was observed via anti-crossing of the upper energy sublevels of 57 Fe nuclei...