Nasal diphthongs are quite rare in the world's languages. This paper analyzes how speakers control articulatory movements for nasal diphthongs in Brazilian Portuguese (BP). Our aim is to characterize the oral-nasal coupling in posterior nasal diphthongs from the Paulistano dialect spoken in the city of Sao Paulo. We show that oral and nasal diphthongs have different tongue contours, besides velopharyngeal coupling. A 2D EMA study was carried out to contrast [aw] and [ãw ̃] in monosyllabic words.