Glutamine synthetase (GS) is an enzyme that controls nitrogen metabolism, which can reduce the concentration of free ammonia in the body. It is utilized by some cancer cells to enhance their growth and proliferation. This project aims to evaluate the effects of GS overexpression on ammonia concentration. To achieve GS overexpression in vivo, we performed both hydrodynamic injections of EF1α-GS plasmids into the mouse's tail veins and an adeno-associated virus containing GS overexpression vectors. Results showed that hydrodynamic tail vein injection achieved slight overexpression of GS in both protein and mRNA levels, whereas AAV-treated mice showed no overexpression of GS.