子宫环（英文名：Intra-uterine device，简称IUD），医学上称为宫内节育器，俗称节育环、避孕环。是一种避孕工具，一般为T形，由医生或其他专业人员在月经期间放入子宫，在有效期内可起到避孕效果。

避孕环一般含有激素或铜。在合格的产品和专业人员放置的情况下，避孕环是一种相对安全有效的避孕方式。全世界有近1.8亿名妇女使用，其中超过三分之二在实行计划生育的中国大陆。中国大陆2012年实施995万（另一统计为720万）例放置宫内节育器手术（俗称上环）和180万（另一统计为284万）例取出宫内节育器手术，造成480例子宫穿孔和1952例感染，已婚育龄（50岁以下）妇女中宫内节育器使用人数达1亿3185万人。宫内节育器是中国大陆的首要避孕措施，在所有避孕措施中使用率占54%，是避孕套的5倍多。

An intrauterine device (IUD or coil) is a small contraceptive device, often 'T'-shaped, often containing either copper or levonorgestrel, which is inserted into the uterus. They are one form of long-acting reversible contraception which are the most effective types of reversible birth control. Failure rates with the copper IUD is about 0.8% while the levonorgestrel IUD has a failure rate of 0.2% in the first year of use. Among types of birth control they, along with birth control implants, result in the greatest satisfaction among users. As of 2007, IUDs are the most widely used form of reversible contraception, with more than 180 million users worldwide.