In a Human body the cell that grows out of control forms a tumour called cancer. The tumour found in the lungs is named after it as lung cancer which endangers the human life the early identification increase the patient’s survival in this world. For detection of lung nodules Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) are the computer aided diagnosis techniques are used. This paper mainly discuss about the pre-processing and segmentation process. Pre-processing step focus to reduce the noises in CT images and segmentation refers to the process of partitioning the pre-processed CT image into multiple regions. Further this paper briefly explains feature extraction and classification.