Vrelo Cave is the deepest cave in Macedonia, located in the canyon Matka which is home to many endemic species not found anywhere else in Europe. Until now, Vrelo Cave has not been investigated in terms of its composition and biodiversity. The purpose of this study was to offer some preliminary data for physical and chemical parameters of water and sediments from Vrelo Cave, as well as its microbiological diversity. Samples were taken from 5 locations. They were analysed for a wide array of physico-chemical parameters, macro- and microelements and concentration of selected organic pollutants. All samples were investigated for several groups of bacteria, yeasts and moulds by a conventional selective media approach. Molecular identification of the isolated bacterial species was done by sequencing of the bacterial 16S ribosomal RNA gene. Regarding the total dry components, total hardness, dissolved oxygen, biochemical and chemical consumption of oxygen, water from Vrelo Cave belongs to Class I. All of the investigated groups of microorganisms except anaerobic sporogenic bacteria were present in water and sediment samples. Notably, a large number of coliformic bacteria (total and faecal) were isolated from all of the investigated samples which classify this water in Class IV, as ecologically unsuitable drinking water. Most of the identified non-coliformic bacteria belonged to the genus Bacillus. We have also identified representatives from Staphylococcus, Proteus, Brevundimonas and Enterobacter. Overall findings suggest a possible connection between the water from the cave and surface waters. Further investigation should be performed to determine the origin of these waters.