Mareham le Fen (otherwise Mareham-le-Fen) is a village and civil parish about 6 miles (10 km) south from the town of Horncastle, Lincolnshire, England.

[3] The parish church is dedicated to St Helen, and is a Grade II* listed building of greenstone and dating from the 13th century.

In the north aisle is a tomb to James Roberts who died 1826, and sailed in the Endeavour with Captain Cook and Sir Joseph Banks.

[5][6] The Grade II listed Royal Oak public house has a datestone of 1473, but is believed to date from the 17th century, with 18th- and 20th-century additions.

[10] Mareham le Fen Victory Silver Band, established in 1919, plays in the local area at events and services.