Nico Ditch (occasionally Mickle Ditch or Nikker) is a six mile (9.7 km) long linear earthwork running between Ashton-under-Lyne and Stretford in Greater Manchester, England. It may have been dug as a defensive fortification, but more likely it was intended to be a boundary marker. It was constructed some time between the 5th and 11th centuries AD.
The ditch is still visible in short sections, such as a 300-metre stretch in Denton golf course. In the parts which survive, the ditch is 3–4 metres wide and up to 1.5 metres deep. Part of the earthwork is protected as a Scheduled Ancient Monument.