Abstarct: A sudden change in the flow rate brings about significant pressure oscillations in the piping system known as water hammer (fluid hammer). Unsteady flow of a non-Newtonian fluid due to the instantaneous valve closure is studied. Power law and Cross models are used to simulate non-Newtonian effects. Firstly, the appropriate governing equations are derived with respect to non-Newtonian fluid constitutive equations and then, they are solved by two numerical approaches. A fourth-order Runge–Kutta scheme is used for the time integration and the central difference scheme is employed for the spatial derivatives discretization. Method of characteristics is another numerical method that employed for solving two dimensional equations. At the end of this section pipe wall structural equations added to basic equations to consider fluid structure interaction effects. To verify the proposed mathematical models and numerical solutions, comparisons with corresponding experimental results from literature are made. The results reveal a remarkable deviation in pressure history and velocity profile with respect to the water hammer in Newtonian fluids. The significance of the non-Newtonian fluid behavior is manifested in terms of drag reduction and line packing effect observed in the pressure history results. Fluid structure interaction results show significant changes in pressure time history and other flow specifications. So modeling fluid structure interaction is inevitable.