Abstract: The most fatal disease in the era of medical science is the brain tumor.it can be diagnosed if detected at the early stage of the tumor growth. Various techniques are developed & has been applied on magnetic resonance imaging to detect the abnormality in the brain as tumor. The segmentation of these magnetic resonance images is very difficult then natural images.

Keywords: Multi-Thresholding, Brain Magnetic Resonance Imaging, Ant Colony Optimization.