Phytocoenological traits of forests of sessile oak in the area of Zrinska Gora were investigated in 2009. Phytocoenological research was conducted using a method of the Zurich-Montpellier School. A comparison was made with acido-thermophilic forests of sessile oak from central and north-western Croatia, then from Slovenia and the Mescek Mountains in Hungary. A statistical comparison was made by entering all the phytocoenological relevés into the Turboveg database. This was followed by a classical synthetic analysis of the phytocoenological relevés and a multivariate analysis using Syntax 2000 software. Average Ellenberg’s values were calculated for each relevé with JUICE 6.3 software . The obtained data were processed with STATISTICA 8.0. Taking into consideration all the facts it can be concluded that the newly established association Potentillo micranthae-Quercetum petraeae shows a high degree of independence and differentiation from other similar associations described to date. In relation to others, it is poorer in species, both in terms of systematic categories to which it belongs and the number of elements from the orders of Fagetalia and Quercetalia pubescentis. Of the species occurring in acidophilic forests of sessile oak, Genista tinctoria, Chamaecytisus hirsutus and Dicranella heteromalla can be considered characteristic species, whereas Galium sylvaticum, Cephalanthera longifolia, Dianthus armeria and Viola alba can be termed differentiating species. The species Potentilla micrantha, Festuca drymeia and Luzula forsteri are very important for the structure, physiognomy and syndynamics of the association. It is subordinated to the alliance Quercion robori-petraeae, the order Quercetalia robori-petraeae and the class Querco-Fagetea.