Mammary gland cancer is the most frequent Malignant tumor in human females and bitches and morbidity and mortality due to it continue to increase. Mammary gland carcinomas are quite heterogeneous in terms of morphology and biological behavior. Twenty-three female dogs were confirmed affected by mammary tumors during the period January 2014 - June 2015. In this study were used different stained technuques in mammary gland tumors of bitches to help us in diagnosing of them. The aim of this study was to compare H-E technique and Masson Trichrome staining technique in mammary gland tumors, in order to differentiate histological types of neoplastic lesions.