In a vehicle license plate identification system, plate region detection is the key step before the final recognition. This paper presents a license plate detection algorithm from complex background based on histogramming and mathematical morphology. The proposed algorithm consists of two main modules: license plate region?s rough detection and license plate exactly location. The former characterized by vertical gradients detection extracts candidate regions from an input image, while the latter conceptualized in terms of mathematical morphology aims to locate the license plate fast and accurately. Experiments have been conducted for this algorithm, and 360 images taken from various scenes were employed, including diverse angles, different lightening conditions and the dynamic conditions. The algorithm can quickly and correctly detect the region of license plate and the license plate detecting rate of success is 97.78%.