The Piano Key Weir (PKW) has emerged as a cost effective and viable solution for dam rehabilitation and new projects with high level of space constraints. The geometrical dimensions of PKW are main factors affecting their discharging capacity. Since, it is a relatively new type of weir that has only been developed in recent years, the description of the effect of its geometrical parameters is still immature. The geometric designs of these weirs presented in the literatures incorporate only linear floor slope of the keys. For better understanding of the influence of curvilinear shapes of outlet key slopes on discharge capacity, an experimental study was conducted. In general, the results showed that PKW with ogee shaped outlet key is more efficient than the linear shaped counterpart for heads higher than its design head. The maximum increase in coefficient of discharge of weir model with curvilinear outlet key in comparison to model with linear outlet key was 5.2%.