中士是军人的职衔，士官的一种，在大多数国家的军衔制度中，中士之下的阶级为下士，中士之上的阶级为上士。

军队编制上多以士官长、上士担任副排长，中士担任班长，下士担任副班长，下辖三到四个伍，可以用军阶较低的人员担任高端职务，称为「占缺」。

****的士官（包含士兵）共分九级，中士相当于美国陆军的Sergeant、空军的Staff Sergeant、或海军的Petty Officer 2nd Class

Sergeant, (normally abbreviated to Sgt) is a rank used in many armies, police forces, and other uniformed organizations. Its origins are in the Latin serviens, "one who serves", through the French term sergent.

The term "sergeant" refers to a Non Commissioned Army Officer placed above the rank of a Corporal and a Police Officer immediately below a Captain. In most armies the rank of sergeant corresponds to command of a squad (or section). In Commonwealth armies, it is a more senior rank, corresponding roughly to a platoon second-in-command. In the United States Army, sergeant is a more junior rank corresponding to a four-man fireteam leader.