Electronic and photocatalytic properties of single-layer Bismuthene nanosheets have been investigated as a function of their sizes. It is shown that Bismuthene nanosheet photocatalytic characteristics are comparable with the currently available high-ranked photocatalysts. The mentioned characteristics are enhanced by the extension of nanosheet along both edges. The nonlinear optics (NLO) analysis for a variety of nanosheet sizes displays a wide range of absorption on the solar spectrum. This would be another fascinating characteristic of water-splitting. The stability of the Bismuthene nanosheet falls by widening the nanosheet from both sides of Armchair and Zigzag edges. The variation of the energy gap between HOMO and LUMO levels concerning the nanosheet width along both Armchair and Zigzag directions has been explored up to 388 atoms. Regions of chemical activity in Bismuthene are mainly focused in the middle of nanosheets. This means that either of Armchair and Zigzag edges in Bismuthene nanosheet demonstrate a negligible chemically activity.