ABSTRACT: The Milada Cave and its underground hydrological system is one of the most important systems of Silická Plateau in Slovak Karst. This article characterizes this system and presents first results of hydrogeochemical research that was realised there during time period 2007 – 2010. The article evaluates chemical composition and microbiological properties of karst waters in the system. The article assesses and compares chemical composition and quality of water in the input and output of the system, compares water of underground stream and seepage water, evaluates the potential of karst water for formation of cave speleothems. All waters of cave and its underground hydrological system represent water with carbonate mineralization, Ca-HCO3 genetic type with A2 exceeds 82 meq %, with some differences of chemical composition. The biggest differences are between water of underground stream and seepage water. Authors point out to the influence of ponors activity that has a negative impact on cave water quality in connection with anthropogenic pollution.