Planktonic and benthic foraminifera were studied in a section, south of Ilam in order to assign palaeobathymetry and the changes through sedimentation course of the Gurpi Formation. The formation consists of 213m marl with intercalation of limy marl with two formal members of Seymareh (Lopha) and Emam-Hasan. The Seymareh Member is made up of Limestone and Emam-Hasan Member is argillaceous limestone. The formation was deposited from middle Campanian through late Paleocene according to the planktonic foraminifera recorded. For the benthic foraminifera, percentage of hyaline, agglutinated calcitic and noncalcitic also epifaunal and infaunal were calculated. A depth of over 800m was assigned for most parts of the formation according to planktonic/epibenthic ratio and the regression equation (D=e(3.58718+(0.03534×%P))). Study of depth indices benthic foraminifera also confirm the depth gained by the regression equation. The relative sea-level curve resulted in from this study is well in accord with the existing eustasy curves indicating the great effect of eustasy on relative sea-level changes against the other factors.