Weirs are important hydraulic structures and are structured for flow measurement, flood control in reservoirs and water level control in open channel and irrigation systems. The most common types of weirs are the sharp crested weir, the circular crested weir, the labyrinth weir and the ogee crest weir. In present study, the quarter-circular crested weir is introduced and investigated. This weir is geometrically consisted of a quarter-circular crest of radius R , an upstream sloped face and a vertical downstream face. The upstream face is tangent on the crest surface and the downstream face must well be ventilated. The hydraulic characteristics of this weir such as discharge coefficient, crest section velocity and pressure profiles, pressure distribution on the crest surface, upper and lower nappe profiles and pool water depth were experimentally measured. The analytical methods of dimensional analysis, momentum, and differential analysis were also used to determine the hydraulic characteristics of quarter-circular crested weir. Using dimensional analysis and momentum methods, the dimensionless hydraulic parameters that affect the discharge coefficient of quarter-circular crested weir were determined. Using the differential analysis method, discharge coefficient and crest section velocity and pressure equations of circular crested weir and quarter-circular crested weir were obtained. In comparison with the other theories, obtained equations for circular crested weir predict the discharge coefficient and the crest section velocity of this weir with the better precision. In the range of conducted tests, discharge coefficient of quarter-circular crested weir was a constant value and equal to 1.261. It is 13 percent larger than the discharge coefficient of sharp crested weir. In comparison with the circular crested weir, the quarter-circular crested weir has the better hydraulic performance. The quarter-circular crested weir can be used in open channels and small diversion dams. In a summary, the large coefficient of discharge, the significant energy dissipation, the accurate measurement of discharge, the large application range and the ease to pass floating debris are the most important benefits of quarter-circular crested weir. Keywords: Quarter-circular crested weir, Circular crested weir, Discharge coefficient, Dimensional analysis, Differential analysis, Momentum