Plentzia (Spanish: Plencia) is a town and municipality located in the province of Biscay, in the autonomous community of the Basque Country. The town has 4,146 inhabitants (2008).

Plentzia is a resort town with a large beach beside the Plentzia River estuary, in the round, shell-shaped Bay of Plentzia, shared with neighbouring Gorliz and Barrika. The beach is very popular as it is clean and the sea is calm due to the shelter of the bay and the town has many amenities for visitors.

Plentzia and its neighbouring municipalities are popular locations for better-off families from Bilbao to buy weekend–holiday homes and during the summer months the town's beach and bars and restaurants become much busier thanks to these residents and other visitors from Bilbao.

As in most Basque towns, Plentzia has a number of restaurants and bars ranging from small bars offering pintxos to restaurants with formal dining. There is also a small Council-run museum telling the town's history and in particular dealing with its history as a merchant marine port. The town also has an indoor municipal Jai Alai Fronton where the traditional Basque sport of pelota is played and competitive matches can often be seen.