准尉是军人的职衔，地位介于军官与士官之间，经上级选拔推荐、军官教育合格后可晋升为少尉。在某些国家的军队制度中，准尉是士官能够晋升的最高官阶；另外在其他国家的军制中，独立成一阶级，或者尚未被授阶成为少尉的军校毕业生、也以「准尉阶级」见习。

英文军阶的warrant officer通常翻译为准尉，因为warrant officer的地位也介于军官与士官之间，然而各国warrant officer的制度、执掌略有不同。

在大日本帝国时期的军衔制度中，类似阶级在陆军是称作特务曹长，在海军称为兵曹长。

A warrant officer (WO) is an officer in a military organisation who is designated an officer by a warrant, as distinguished from a commissioned officer who is designated an officer by a commission, and a non-commissioned officer who is designated an officer, often by virtue of seniority.