The objective of this study was to investigate the correlation between different histological types and grades of canine malignant mammary tumours, tumour cell proliferation and their angiogenic activity using immunohistochemical markers. Mammary tissue samples from 47 bitches with mammary cancer were evaluated. The expression of cellular proliferation marker Ki-67 and endothelial marker Von Willebrand's factor (vWF) were immunohistochemically demonstrated. The tumours with the highest Ki-67 and vWF expressions were found to share similar histomorphological features. Simple solid carcinoma had the highest levels of Ki-67, vWF, and higher histological grade while complex carcinomas, osteosarcomas, and carcinosarcomas had the lowest ones. The differences between the expressions of Ki-67 and vWF in different tumour types were considered to be of great importance in determination of biological behaviour and prognosis of these tumours. This study is one of the few studies that evaluate these differences among the subtypes of malignant canine mammary tumours.