Mark XIII or Mark 13 often refers to the 13th version of a product, frequently military hardware. "Mark", meaning "model" or "variant", can be abbreviated "Mk."

Mark XIII or Mark 13 may refer to:

Science

• Kallikrein 13 or mK13, a protein

Military and weaponry

• Mark 13 torpedo, US Navy's most common air-dropped torpedo in World War II
• Mk XIII railway gun, a variant of the British BL 9.2-inch railway gun
• Supermarine Spitfire PR Mk XIII, lightly armed low-altitude Rolls-Royce Merlin-powered reconnaissance aircraft, first tested March 1943
• Vickers Wellington GR Mk XIII, 1944 Coastal Command medium bomber with ordinary nose turret, mast radar and no waist guns
• De Havilland Mosquito NF Mk XIII, a night fighter variant of the De Havilland Mosquito that replaced nose guns with radar
• Mark 13 nuclear bomb (1951–1954), an American experimental weapon that never entered service
• Centurion Mk 13 (1959–1962), a British main battle tank fitted with infrared equipment and a ranging gun
• Mk 13 missile launcher, a single-arm guided missile launching system
• Mk 13 Mod 0 or EGLM (2004), a 40 mm grenade launcher
• MK 13 rifle, a US Military sniper rifle
• MK13-class missile boat, a vessel of the Iranian Islamic Revolutionary Guard Corps Navy

Technology

• Cooper Mk XIII (1959), a Cooper 500 cc rear-engined racing car

Other uses

• Mark 13 and Mark XIII, the thirteenth chapter of the Gospel of Mark in the New Testament of the Christian Bible
• M.A.R.K. 13, the fictional killer robot in the 1990 film Hardware