LAUSR

2D bismuth oxyselenide (Bi2O2Se) with high electron mobility is advantageous in future high‐performance and flexible electronic and optoelectronic devices. However, transfer of thin Bi2O2Se flakes is rather challenging, restricting measurements of its mechanical properties and application exploration in flexible devices. Here, a reliable and effective polydimethylsiloxane (PDMS)‐mediated method that allows transferring thin Bi2O2Se flakes from grown substrates onto target substrates like microelectromechanical system substrates is developed. The high fidelity of the transferred thin flakes stems from the high adhesive energy and flexibility of PDMS film. For the first time, the mechanical properties of 2D Bi2O2Se are experimentally acquired with a nanoindentation method. It is found that few‐layer Bi2O2Se exhibits a large intrinsic stiffness of 18–23 GPa among 2D semiconductors, and a Young's modulus of 88.7 ± 14.4 GPa, which is consistent with the theoretical values. Furthermore, few‐layer Bi2O2Se can withstand a high radial strain of more than 3%, demonstrating excellent flexibility. The development of the reliable transfer method and documentation of mechanical properties of 2D Bi2O2Se jointly fill the gap between theoretical prediction and experimental verification of mechanical properties of this emerging material, and will promote flexible electronics and optoelectronics based on 2D Bi2O2Se.