Recent results have shown that Newtonian liquid curtains become more stable as the viscosity rises. However, the effect of shear thinning rheology on the dynamics of curtain breakup is not well understood. The role of shear thinning behavior on liquid curtain stability was studied by high-speed visualization. The critical condition at the onset of curtain breakup was determined by identifying the flow rate below which the curtain broke. Curtain breakup was seen to begin with a hole initiated within the curtain. The results reveal that the dynamics of curtain breakup is governed by the shear viscosity at a characteristic deformation rate and, as in the Newtonian liquid case, the stability increases as the characteristic viscosity rises.