Nuclei segmentation of the epithelial cells of a Pap smear image is an important step in order to have correct morphometric measures. This task is non trivial due to the complexities of the Pap smear images. Our paper presents a novel method on nuclei segmentation using morphological operation and watershed transformation. The proposed segmentation method was evaluated with respect to its nuclei area and its shape-similarity in comparison to the pathologist truth. It showed that the segmentation results are promising and it can be used for further analysis such as cell quantification or abnormality cell detection.