<p>This study investigated the effects of deep cryogenic treatment (DCT) on hot isostatic pressed (HIP) beryllium for inertial devices, focusing on residual stress, microstructure, tensile properties, and dimensional stability. The findings revealed that during DCT, residual stress in beryllium increased gradually due to non-uniform volumetric contraction and mismatch stress, reaching a 59.9% increase from initial levels after 200 h of DCT. DCT led to significant grain refinement and an increase in dislocation density. In 200 h DCT-treated beryllium, geometric necessary dislocation (GND) density increased 17.9%, grain size decreased 12.3%, and therefore yield strength and tensile strength improved by 4.2% and 5.6%, respectively. The dimensional stability of HIP beryllium was significantly enhanced by DCT, and the improvement tended to increase with the duration of DCT. The cumulative size changes of beryllium after 200 h of DCT during both cold exposure and cold cycling decreased significantly by 86% and 50%, respectively, compared to those of HIP beryllium. Furthermore, the residual tensile strength and retention rate increased by 12.5% and 5.5%, respectively, after undergoing room-temperature creep at 100 MPa for 1000 h.</p>