Abstract: Petrological and geochemical features at the Slani potok's stream spring (located on Medvednica mountain) were explored. Eight lithofacies (L1 – Lithofacies of limestone with fossils; L2 – Lithofacies of quartzite; L3 - Lithofacies of light gray limestone; L4 - Lithofacies of dark gray dolomite and dolomite breccia; L5 - Lithofacies of ooidic limestone; L6 - Lithofacies of dark red clastics; L7 - Lithofacies of recrystallized limestones; L8 - Lithofacies of low to middle grade metamorphic rocks) are determnied by field work and micropetrographic analysis. Micropetrographic analysis of rocks in the area around Slani potok spring were made. Physical and chemical characteristics of stream water were analyzed as well. Good correlation between petrological characteristics of the rocks in the study area and geochemical characteristics of water from Slani potok has been determined. Chemical analysis of water from the spring area and Salt Mine site showed extremely elevated electrolyte content, especially for sodium and magnesium. These indicators confirm the existence of mineral halite within the carbonate rocks in Salt mine (near the Slani potok spring), where water gradually dissolves halite, and rises to the surface. The water of the Slani potok in the spring area is of sodium-chloride type, while downstream water changes to calcium-bicarbonate type. X-ray diffraction analysis confirmed the existence of gypsum and halite within carbonate rocks from the spring area. All the results confirm the hypothesis that the petrological characteristics of the rocks in the spring area of Slani potok have a significant impact on geochemical characteristics of stream water.