We report bulk superconductivity at 2.5K in LaO 0.5 F 0.5 BiSe 2 compound through the DC magnetic susceptibility and electrical resistivity measurements. The synthesized LaO 0.5 F 0.5 BiSe 2 compound is crystallized in tetragonal structure with space group P4/nmm and Reitveld refined lattice parameters are a= 4.15(1)Å and c=14.02(2)Å. The lower critical field of H c1 = 40Oe, at temperature 2K is estimated through the low field magnetization measurements. The LaO 0.5 F 0.5 BiSe 2 compound showed metallic normal state electrical resistivity with residual resistivity value of 1.35mΩ-cm. The compound is type-II superconductor, and the estimated H c2 (0) value obtained by WHH formula is above 20kOe for 90%ρ n criteria. The superconducting transition temperature decreases with applied pressure till around 1.68GPa and with further higher pressures a high T c phase emerges with possible onset T c of above 5K for 2.5GPa. [3][4][5][6][7][8][9][10]. The highest T c =10.6 K has been obtained for LaO 0.5 F 0.5 BiS 2 superconductors under hydrostatic pressure [11]. In particular, the T c of REO 1−x F x BiS 2 (RE=La, Ce, Nd, Pr) [11][12][13][14] and Sr 1−x RE x FBiS 2 (RE = La, Ce, Nd, Pr, Sm) systems, enhances tremendously by applying the hydrostatic pressure [15,16]. As far as the chemical substitutions are concerned the doping of Se on the S site in the Bi 4 O 4 S 3-x Se x and NdOFBiS 2-x Se x superconductors showed the suppression in T c [17,18]. Interestingly, the superconductivity at 2.5K in BiSe 2 based layered LaO 0.5 F 0.5 BiSe 2 polycrystalline compound has recently been reported by A. at. el,[19]. The crystal structure of the superconducting oxyselenide is similar to other layered superconducting compounds such as CuO based cuprates and iron-based Pnictides with alternating stacks of blocking and superconducting layers [19]. Soon after this report, superconductivity with T c value of 3.0K was reported in LaO 0.5 F 0.5 BiSe 2 single crystals [20]. Also, the theoretical approaches were applied, and it was shown that the electronic structure, lattice dynamics, and electron-phonon interaction of the newly discovered superconductor LaO 0.5 F 0.5 BiSe 2 is that same as that for LaO 0.5 F 0.5 BiS 2 compound [21]. The pressure effect on LaO 0.5 F 0.5 BiSe 2 single crystals showed a decrease in T c with applied pressure of up to 1.75GPa and obtained high T c phase (6K) for higher pressure (> 1.97GPa) [22]. This is strikingly different than the impact of hydrostatic pressure on similar structure oxy-sulfides, where T c increases profoundly with pressure [11][12][13][14][15][16]. The external pressure effect is a conventional method for structural modulation that is often used to change the superconducting T c . For example, the increase in T c of LaO 0.5 F 0.5 BiS 2 compound under pressure is due to a structural phase transition from tetragonal phase (P4/nmm) to monoclinic phase (P21/m) [23].Here we report the successful synthesis of polycrystalline LaO 0.5 F 0.5 BiSe 2 compound through the solid state reaction method. The ...