PCNA is synthesized in early G1 and S-phases of cell cycle. Tight linkage to cell proliferation has led to the investigation of its role in the evaluation of tumors for prognosis. The aim of this study is to use computerized image analysis to measure PCNA and CD31 antibodies in a series of canine melanocytic tumors to assess density of marked cells by these antibodies, and to correlate density of marked cells with malignant degree of these tumors through comparative study between CD31, PCNA and microscopic aspect. 12 dog melanic tumors were diagnosed during the period 2001–2010 in Pathology Department USAMV Cluj-Napoca, for PCNA expression study, and 10 samples of them were treated with CD31 marker by immunohistochemical for comparative study.