The discovery has been made in the grounds of Soulton Hall near Wem by specialists, The Dig Venturers, working with students from Cardiff University.
Tim Aston, whose family own Soulton Hall, said it was thrilling news.
He said the mound on which the dig was made had been left untouched by the family as they had always wondered what lay beneath. It had been a playground for children in the family.
The Dig Venturers visited Soulton Hall in 2019 for a test dig and returned last week, digging a strip of land around the edge of the mound.
Site manager at the dig, Nat Jackon, said: "We found what we think what might be a castle on the mound. There seems to be a substantial wall and blocks of wood dating back to somewhere between the 13th to 15th century.
"To find this is just amazing. "We think it was a small castle, which dominated the road to Wem.
"There would have been a moat around it and and we believe we have found evidence of the bridge that went over the moat. But that will be for further exploration."
The group worked alongside members of Cardiff University on the dig with the archaeologists praising the students for their hard work.
"This was the first excavation for them, the first time they have been out on a dig together. We are hoping to work with them again next year."
As well as remnants of the castle structure the dig also found artefacts.
These included pottery fragments, a pilgrim's badge and an ampula, which was used to carry holy water on pilgrimages.