Lielupe (Latvian) 'big river'; in German Kurländische Aa, (see Aa River) is a river in Latvia.

Its length is 119 km, along with Memele 310 km. The surface area of its basin is 17,600 km².

Lielupe begins at the joining point of the rivers Memele and Musa. At its lower reaches it flows parallelly to the coast line of the Gulf of Riga. Lielupe falls into the Gulf of Riga, while a branch of its falls into the Daugava river.

Lielupe is navigable in the range of 100 km.