The plans for Hopwas Wood near Tamworth have been submitted by Lafarge Tarmac to the county council.
Austin Brady, of the Woodland Trust, said such woodlands were irreplaceable, adding that "turning this into a hole in the ground is bad for everybody".
The company said the quarry would cover only a fifth of the wood.
It also claims much of the area where it proposes to extract sand and gravel for the construction industry was damaged by fire in the 1970s and can no longer be considered ancient woodland.
Opponents of the plans include Tamworth Tory MP Christopher Pincher who said he would encourage residents to complain to the County Council before a 5 December deadline.
Mr Brady, the Trust's director of conservation, said it regarded the plans as the "largest threat to a single ancient woodland site in England that the charity has seen in its 42-year history".
Such historical woodland covered only 2% of Britain, said Mr Brady, and often contained rare and threatened species.
"What we're concerned about is that people are putting profits before the long term importance of the environment for society," he said.
The Trust maintains a loophole in current planning policy meant protection for ancient woodland was "weak" and cites a decision by Communities Secretary Eric Pickles to approve a quarry on "ancient woodland" near Maidstone.
This was denied by a government spokesman who said planning policy made it clear such development should be avoided.
The plans for the 76-acre site (31 hectares) have been added by Lafarge Tarmac to the county's Minerals Local Plan, which covers the period until 2030.
The firm said the local community would be consulted about the plans and has pledged to restore the land to its natural habitat.
Plans to turn an area of ancient woodland mentioned in the Domesday Book into a quarry have angered conservationists in Staffordshire.