Gmina Grudusk is a rural gmina (administrative district) in Ciechanów County, Masovian Voivodeship, in east-central Poland. Its seat is the village of Grudusk, which lies approximately north of Ciechanów and north of Warsaw.
The gmina covers an area of , and as of 2006 its total population is 3,892 (3,823 in 2013).
Gmina Grudusk contains the villages and settlements of:
Gmina Grudusk is bordered by the gminas of Czernice Borowe, Dzierzgowo, Regimin, Stupsk and Szydà Âowo.