In this Thesis, systematic research of spontaneous precipitation of calcium oxalate in the artificial urine system with increased complexity mimicking the conditions of hyperoxaluria was conducted. The precipitation systems have been optimized in order to emulate physiological and pathological conditions (\( \theta = 37^{\circ}C \), \(pH_{i} \) = 5.0 and \(pH_{i} \) = 9.0) over a wide range of initial reactant concentrations of calcium (2.0 mmol \(dm^{-3} \) ≤ \(c_{i}\left ( Ca^{2+} \right )\) ≤ 10.0 mmol \(dm^{-3} \)) and oxalate (0.6 mmol \(dm^{-3} \) ≤ \( c_{i}\left ( C_{2}{O_{4}}^{2-} \right )\) ≤ 8.0 mmol \(dm^{-3} \)) with the aim of establishing hyperoxaluria conditions. The main aim of this research is to investigate the effects of system complexity, initial \(pH_{i} \) and reactant concentration on precipitation and morphology of calcium oxalate under pathological conditions. In all precipitation systems, dominant precipitation of calcium oxalate monohydrate (COM) was observed, except in the artificial urine system at \(pH_{i} \) = 9.0, in the concentration range \( c_{i}\left ( C_{2}{O_{4}}^{2-} \right )\) ≥ 6.0 mmol \(dm^{-3} \) and \(c_{i}\left ( Ca^{2+} \right )\)≥ 7.5 mmol \(dm^{-3} \) where a mixture of COM and calcium oxalate dihydrate (COD) precipitated. The significant difference in crystal morphology was observed: irregular crystals with pronounced aggregation tendency have precipitated in the artificial urine, particularly in the systems with increased supersaturation.