Rich foraminiferal assemblages from the Lower/Middle Devonian parastratotype at the Prastav Quarry near Prague (Barrandian area, Czech Republic) were studied in detail and correlated with foraminifers from seven sections of the same age from the Barrandian area. Forty-five taxa of foraminifers were recognized in the Lower/Middle Devonian boundary beds. Distribution of foraminiferal taxa in sections and their comparison with the respective paleoecological data show good potential for Devonian foraminifers to be used as paleoecological indicators. Psammosphaera cava, Pseudoastrorrhiza cf. irregularis, Saccorhiza pseudospiralis and Thuramminoides sphaeroidalis could tolerate unfavorable ecological conditions. Psammosphaera and Hemisphaerammina occurred in higher energy environments, while Ammodiscus ex gr. incertus required a low-energy environment. Morphometric variability of Ammodiscus ex gr. incertus (test size, number of whorls, size of proloculus) may indicate the presence of megalospheric and microspheric forms. Microspheric forms prevailed in unstable, higher energy environments. Multivariate analyses of foraminiferal assemblages enable differentiation of four types of foraminiferal assemblages whose spatial distribution corresponds well with lithofacies distribution. Changes in successive assemblages mirror shifts from low-energy to higher energy environments around the Lower/Middle Devonian boundary (= Basal Choteč Event).