Sheet-like nanocrystalline SnSe with an orthorhombic phase has been prepared via a reaction between a selenium alkaline aqueous solution and tin (II) complex at room temperature under atmospheric pressure. The XRD pattern indicated that the selenium alkaline solution as a selenium source, made the product to crystallize well at room temperature. The XPS analysis indicated that the purity of the product was quite high. The mechanism of the formation of tin (II) selenide was discussed.