Ceterach officinarum D.C., Asplenium trichomanes L. and A. adiantum nigrum L. occur in the fissures of precipitous calcareous rocks in the Gorge of Sićevo. Here, humus rhizosphere soil, i.e. Lithosol, mainly consisting of the leaf and root remains of the ferns in different degradation phases gets formed. The present study was concentrated on determination of total phenolics in the fern leaves, rhizomes and rhizosphere soil and on the analyses of phenolic acids. In the leaves of all three ferns total free phenolics were dominant and exceeded that of their bound forms 1.28–6.95 times. The highest amounts of phenolics were found in the leaves (free of 11 744.00 μg g–1 and bound of 9 135.00 μg g–1, respectively) and rhizomes (free of 2 811.11 μg g–1 and bound 1 962.74 μg g–1, respectively) of Ceterach officinarum. The humus of rhizosphere soil under the ferns was characterized by higher amounts of total bound phenolics (up to 3 873.34 μg g–1). It contained low amounts of free phenolic acids (0.687–9.115 μg g–1). The content of bound phenolic acids exceeded that of their free forms up to 280 times. Since ferns as pioneer species grow at first in the rock fissures either containing no soil or soil in the stage of formation, produces phenolic compounds as secondary metabolites and thus play the significant role in soil and humus formation.