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The study aimed to evaluate the humus quality of anthropogenic soils derived from flysch deposits. A total of 10 samples were collected in the top-soil horizon (0-20 cm) of olive groves in Kaštela Bay in Middle Dalmatia, Croatia. Five samples were taken from traditional low-input olive groves (TOG), and the other five samples were from intensive ones (IOG). The soil samples were analysed for basic soil properties: particle size distribution, pH, carbonate content, P2O5, K2O, and soil organic carbon (SOC) content. Humic substance isolation was done following the procedure given by Schnitzer (1982). Spectroscopic characterization of humic substances was carried out by measuring absorbances in VIS spectral range (400-700 nm). Optical index E4/E6 (ratio of optical absorbance at 465 and 665 nm for humic substances in solution) was calculated. The mean value of SOC content in soils of TOG was lower than in soils under IOG (1.20 and 1.60%, respectively). The absorption spectrum of the studied soils showed a monotonous decrease of absorbance from 400 to 700 nm. The E4/E6 indices for soils under TOG varied from 4.60 to 5.00, while for soils under IOG were in the range of 4.83 - 6.89. The E4/E6 indices > 4 revealed low humus quality in studied soils. However, soils under TOG have lower mean values E4/E6 index in comparison to soils under IOG (4.76 and 5.70, respectively), indicating slightly higher humus quality. [ABSTRACT FROM AUTHOR]