A 81mm Mortar is a medium weight mortar. It is a smooth bore, muzzle-loading, high-angle-of-fire weapon used for long-range indirect fire support to light infantry, air assault, and airborne units across the entire front of a battalion zone of influence.

Many countries use a "81mm Mortar" in their armed forces. Examples are:

• Myanmar - BA-90 Mortar
• United Kingdom - L16 81mm Mortar
• United States - M252 mortar.