The Scottish SPCA was told about the macabre find by police after a member of the public found the head in Bellshill on Monday.
They are uncertain of the circumstances regarding the horse’s death but say it is “sickening” if it was a deliberate act.
Inspector Jack Marshall of the animal welfare charity said: “We can’t be sure of the circumstances surrounding this horse’s death, but if someone has done this as a deliberate act of cruelty then this is sickening.
“The head was found in the burn near the junction between Carnbroe Road and Rosebank Road.
“We’re urging anyone with information to contact our animal helpline in confidence.”
Anyone with information is urged to contact the Scottish SPCA animal helpline on 03000 999 999.