The aim of the study was to determine the whey protein profile, somatic cell count, total bacteria count, chemical composition and some physico-chemical properties of late lactation milk produced by Polish Cold Blooded Horses mares between 141 and 210 days post partum. The whey protein profile, expressed as a percentage of the total sum of the six whey proteins considered, was characterised by high proportions of lysozyme (11.6%), lactoferrin (14.6%) and immunoglobulin (15.8%). Whey proteins represented in greatest amounts included β-lactoglobulin (29.2%) and α-lactalbumin (25.4% of the total whey protein fraction). Mares' milk was characterised by very low numbers of somatic cells and total bacterial counts. Results presented confirm that late lactation mares' milk constitutes a valuable source of bioactive components.