Gmina Pniewy is a rural gmina (administrative district) in Grójec County, Masovian Voivodeship, in east-central Poland. Its seat is the village of Pniewy, which lies approximately 10 kilometres (6 mi) north-west of Grójec and 40 km (25 mi) south-west of Warsaw.
The gmina covers an area of 102.05 square kilometres (39.4 sq mi), and as of 2006 its total population is 4,597.