Gmina Brzeźnio is a rural gmina (administrative district) in Sieradz County, Łódź Voivodeship, in central Poland. Its seat is the village of Brzeźnio, which lies approximately 15 kilometres (9 mi) south-west of Sieradz and 67 km (42 mi) south-west of the regional capital Łódź.
The gmina covers an area of 128.73 square kilometres (49.7 sq mi), and as of 2006 its total population is 6,351.