Pistachio hull (PH) is the main pistachio by-product produced from the pistachio dehulling process. The product consists of 12.7, 5.7, 16.6, 25, and 20% ash, EE, CP, NDF, and ADF, respectively and can be used as a feedstuff for ruminant animals. It is a mount of energy, fibre and potassium (Naserian and Vahmani, 2005). Because its constitutive tannin content can bind protein and cellulose, it was hypothesized that PH tannin can decrease the digestibility of protein. There is no clear consensus amongst researchers on the effect of dried pistachio by product on milk yield, milk composition, rumen fluid pH and N-NH3 concenteration. The main objective of this experiment was to evaluate effects of different sources of supplemental protein with dried pistachio by product on milk yield, milk composition rumen fluid pH and N-NH3 concenteration of dairy cows.