Now a day security is a major issue in public places such as railway stations, airports, shopping malls and in crowded areas. Unattended object detection is one of essential tasks in video surveillance system. This paper proposes an algorithm for detecting unattended and unknown object using background subtraction and morphological filtering. The main goal of the algorithm is to automatically detect the suspicious object and to improve the safety and security of the public areas. The system takes frames from video which is captured by a static camera as input and subtraction of foreground and background is done using thresholding techniques. To improve the detected region, morphological operation is used in the process. The system recognizes the reasons of interest, creates blobs of objects, labels the blobs and finally gives a warning when suspicious objects are detected.