Weirs are structures commonly utilized in water level adjustment and flow control in water passages and hydraulic structures. Labyrinth weirs represent an effective and economic solution for increasing efficiency. These are hydraulic structures that are used for controlling the flow as well as increasing the discharge capacity at a constant width. They can be implemented and applied in plan with triangular, rectangular, trapezoidal or curved geometries. This study used a diagonal circular labyrinth weir in horizontal angles of 60, 70, 80 and 90 degrees. The effect of different labyrinth weir diameters of 15, 20, 25 and 30 cm under different flow rates on the hydraulic performance and discharge Coefficient of the weirs was tested. The results indicated the flow over the weir was of a free flow type from the onset of the tests until the flow rate smaller than 40 lit/sec. When the flow rate in the tests was increased from 40 to 120 lit/sec, the flow above the weir became free and submerged and no air infiltration into the flow was observed. It was also observed that increasing the dimensionless ratio of the total hydraulic head to the diagonal labyrinth weir's height decreased the discharge coefficient of the weir. The highest discharge coefficient was observed in the diagonal weir with a horizontal angle of 60 degrees. The results showed that increasing the ratio of the hydraulic head decreased the flow discharge coefficient in all of the four types of labyrinth weirs studied with diameters of 15, 20, 25 and 30 cm. The highest discharge coefficient occurred in the diagonal weir with a horizontal angle of 60 degrees. The lowest discharge coefficient was observed for the vertical weir. It was also found that increasing the Froude number led to a decrease in the weir's discharge coefficient. The increased Froude number entailed the increased flow head over the weir. Results indicated that increasing the water head upstream of the structure increased the weir over fall an