In this work, we are reporting on the simulation of the beryllium selenide (BeSe) nanowires (NWs) by computational package Q-Espresso / PWSCF according to the ab-initio calculations. Structural and electronic properties, including cohesive energy and Density Of State (DOS) BeSe NWs in two phases on the zinc–blende (ZB) and wurtzite (WZ), using density functional theory based on pseudo-potential approximation and generalized gradient approximation (GGA) up to 20 angstrom in diameter has been calculated. Due to dangling bonds (DBs) in the side surface NWs, cohesive energy is obtained less than the amount of this energy in bulk state of this compound, but with increasing diameter of NWs, the amount of this energy will approach to the bulk state. Comparison of cohesive energy with beryllium selenide NWs in two phases, we find these NWs in WZ phase is more stable and have good compatibility for this result with other results in NWs of similar compounds. The value of energy gap in these NWs on various diameters is obtained less than the amount of the bulk state. It is observed that by increasing the diameter of NWs, the cohesive energy approaches to its value in bulk state.