According to the Washington Post newspaper, the weapons were stored in bunkers in mountains about 40km from the capital, Tirana, and forgotten about after Hoxha died in 1985.
They were later found and declared to the United Nations and United States.
Exposure to Mustard gas can cause severe blisters and result in blindness.
The Chemical Weapons Convention, which came into force in 1997, outlawed the production, acquisition, development or transfer of chemical munitions, and set up a tough verification system for dismantling stockpiles.
Six members of the disarmament agency have declared a total of more than 71,000 metric tonnes of chemical warfare agents and by the end of June 2007 one third of them had been destroyed, the agency said.
The US and Russia control the vast majority of chemical weapons but efforts to eliminate them are behind schedule.