Gmina Nasielsk is an urban-rural gmina (administrative district) in Nowy Dwór County, Masovian Voivodeship, in east-central Poland. Its seat is the town of Nasielsk, which lies approximately north-east of Nowy Dwór Mazowiecki and north of Warsaw.
The gmina covers an area of , and as of 2006 its total population is 19,259 (out of which the population of Nasielsk amounts to 7,364, and the population of the rural part of the gmina is 11,895).
Apart from the town of Nasielsk, Gmina Nasielsk contains the villages and settlements of Aleksandrowo, Andzin, Borkowo, Broninek, Budy Siennickie, Cegielnia Psucka, Chechnówka, Chlebiotki, Chrcynno, Cieksyn, Czajki, Dàbrowa, DÃÂbinki, Dobra Wola, Gà Âodowo Wielkie, Jackowo Dworskie, Jackowo Wà Âoà Âciaà Âskie, Jaskóà Âowo, Kàtne, KÃÂdzierzawice, Konary, Kosewo, Krogule, Krzyczki Szumne, Krzyczki-PieniÃ à ¼ki, Krzyczki-à »abiczki, Lelewo, Lorcin, Lubomin, Lubominek, Malczyn, Mazewo Dworskie A, Mazewo Dworskie B, Mazewo Wà Âoà Âciaà Âskie, MiÃÂkoszyn, MiÃÂkoszynek, Mà Âodzianowo, Mogowo, Mokrzyce Dworskie, Mokrzyce Wà Âoà Âciaà Âskie, Morgi, Nowa Wieà Â, Nowa Wrona, Nowe Pieà Âcirogi, Nowiny, Nuna, Paulinowo, Pianowo-Bargà Ây, Pianowo-Daczki, Pniewo, Pniewska Górka, Popowo Borowe, Popowo-Póà Ânoc, Popowo-Poà Âudnie, Psucin, Ruszkowo, Siennica, Sà Âustowo, Stare Pieà Âcirogi, Studzianki, Toruà  Dworski, Toruà  Wà Âoà Âciaà Âski, Wàgrodno, Wiktorowo, Winniki, à »abiczyn and Zaborze.
Gmina Nasielsk is bordered by the gminas of Joniec, Nowe Miasto, Pomiechówek, Serock, à Âwiercze, Winnica and Zakroczym.