<p>The Romualdo Formation is the sedimentary succession of the Araripe Basin of northeastern Brazil that best records the marine incursion of an epicontinental sea during the Aptian–Albian transition. While the depositional environment of the Romualdo Formation have long been the subject of debate, detailed data on the composition of its microfauna can provide important insights for understanding its formative processes. In the present study, the benthic and planktonic foraminifera of four sections of the Araripe Sedimentary Basin were analysed in order to reconstruct the palaeoecological and palaeoenvironmental conditions of the Romualdo Formation. The foraminifera identified in the present study belong to 13 families, with a predominance of benthic taxa. The families Hauerinidae and Conorboididae were the most abundant overall. The other principal families included the benthic Spirillinidae, Ammodiscidae, Hemigordiopsidae, Vaginulinidae, Ellipsoidinidae, Nodosaridae, and the planktonic family Hedbergellidae was much less abundant. Four assemblages (<i>Quinqueloculina</i>; <i>Quinqueloculina–Conorboides</i>; <i>Quinqueloculina–</i>other groups, and <i>Bathysiphon</i>) were identified here. These assemblages were composed primarily of epifaunal species characteristic of stressful conditions related to marginal marine environments. These assemblages indicate poorly oxygenated environments with low sedimentation rates, associated with the marine transgression that occurred during the late Aptian. The distribution of the foraminiferal assemblages in the Romualdo Formation of the Araripe Basin indicates a progressive shift in environmental conditions as the area evolved into a marine ecosystem.</p>