Polymorphism is a common phenomenon in nature. Here, we report one-pot wet chemical method to synthesize two polymorphs of Au19Ag4(S-Adm)15 nanocluster protected by 1-adamantanethiol (HS-Adm), which adopt P-1 and P21/c space group respectively. The crystal structures of two polymorphs were determined by X-ray crystallography. Compared to the previously reported Au19Ag4(S-Adm)15 nanocluster adopting P21/n space group, polymorphs of Au19Ag4(S-Adm)15 with P-1 and P21/c space group show the different optical properties. Moreover, Au19Ag4(S-Adm)15 with P-1 space group exhibits good thermal stability. Meanwhile, we investigated the effect of solvent and molar ratio of metal precursors on the polymorphs. This work provides an insight to polymorphs of metal nanoclusters.