In this study, the adsorption and dissociation of H2Segas on pristine and transition metal (TM) atoms doped nanosheets have been investigated theoretically using density functional theory (DFT) calculations. To understand the adsorption mechanics, we have examined the adsorption energy, the charge transfer between the adsorbent and adsorbate, the band structure, the density of states (DoS), as well as the optical properties. The structural stability of TM atoms (Fe, Mn)‐ doped BN nanosheets have been verified by finding the cohesive energy. The adsorption energies of H2Se on pristine BN, Fe–BN, and Mn–BN sheets are −0.012, −7.627, and −10.001 eV, respectively; that is, the H2Se gas get dissociated when interacted with the Fe–BN and Mn–BN nanosheets. The relaxed geometrical structures of complexes and electron density difference (EDD) map analysis displayed that the H2Se gas makes bond with TM‐doped nanosheets, that is, dissociated. Furthermore, we viewed the optical properties of the pure, TM‐doped nanosheets as well as the gas‐adsorbed complex structure to demonstrate the adsorption behavior. Therefore, our obtained results demonstrated that the Fe‐ and Mn‐doped BN sheets are good candidates for adsorption and dissociation of H2Se gas.