Piano key weirs are a new type of Weirs that are designed to improve dams discharge capacity. Generally in increasing the upstream head water decreases the discharge capacity this tyre of weir. Thus, in this research, the effect of discontinuous parapet walls with and without slope at the crest was evaluated. Hence, the various lengths                         (0.25, 0.5, 0.75 and 1)  were investigated at the weir with sloped parapet walls. Also two weir height were considered with 0.5 (Model 1) and 1.33 (Model 2). All the experiments of this research were performed in a experimental flume with 10 m length, 0.8 m width and 0.6 m height. The results showed that the weir efficiency increases up to 20 percent in model 1 with un-sloped parapet wall. Moreover, these walls have no significantly effect on the weir efficiency at the more head water in the sloped parapet wall of model 1. Moreover, findings showed that the continuous un-sloped parapet wall increases the discharge capacity up to 4.6 times of linear weirs.