Usage of the terms Pannonian Basin and Pannonian Plain in physical and regional geography is often characterised by vague spatial extent, especially in Serbian geographical literature. The aims of this paper are directed towards establishing a method which would define a plain in geomorphological and geomorphometrical sense. Although the case study is focused on definition of the actual boundary of the Pannonian Plain in Serbia, the method of delineation can be used on other locations as well, especially in the wider area of the Pannonian (Carpathian) Basin. The method relies on the numerical analysis of a digital terrain model, which produced the value of the surface roughness coefficient. By combining the geomorphometrical analysis with spatial extent of characteristic lithologies (Quaternary) and morphological processes (dominant fluvial aggradation and eolian process), the exact delineation of the Pannonian Plain in Serbia was carried out. As opposed to some earlier opinions, the Pannonian Plain extends further to the south from the Sava and the Danube Rivers, encompassing also the lower parts of the Drina, Kolubara, Velika Morava and Mlava basins. Within Serbia, the Pannonian Plain occupies 24,450 km², which is 27.6% of the territory of the country. The elevation ranges from minimal 68.5 m a.s.l. to the maximum of 155 m a.s.l. The mean elevation of the Pannonian Plain in Serbia is 83.5 m a.s.l.