Effects of two types of emulsifying salts on the functionality of Mozzarella cheese were studied.Trisodium citrate (TSC) and trisodium pyrophosphate (TSPP) were added to the stretching water at level of 1%, 3% and 5% during hot-stretching step, respectively. The main composition, textural properties, meltability and free oil content of the cheese prepared were measured, and the rheological behaviors of the cheese were also observed. The results showed that addition of TSC and TSPP significantly affected the meltability of the cheese. Also, hardness, cohesiveness and free oil content of the cheese increased (P<0.05). Meltability content was increased by 37.58% and 59.57% with TSC of 3% and TSPP of 3%, respectively. Addition of the emulsifying salts promoted solubilization of phosphate in the cheese, resulting in proteinprotein interactions decreased and protein-water interactions increased. The results showed that addition of TSC and TSPP into stretching water could significantly improve the functionality of Mozzarella cheese. 