The saCas9 mRNA expresses an wild type Staphylococcus aureus cas9 enzymatic protein. This mRNA is capped with Cap1-AG structure with high capping efficiency. It has 100% substituted with N1-methylpseudouridine for enhanced expression and reduced immunogenicity. The mRNA has a 100A tail in its sequence, mimics a mature mRNA. After efficient delivery, saCas9 mRNA can translate into protein function for gene editing in cells.