硫柳汞（INN：Thiomersal），是一种有机汞化合物，用途为抗菌和抗真菌剂，被用于疫苗、皮肤测试剂、纹身药水等液体的防腐。

其用于疫苗防腐引发争议，有人声称这会导致儿童汞中毒和自闭症，引发部分公众恐慌。但官方宣称并没有合理的证据证明疫苗中微量的硫柳汞对人体有任何害处。目前美国、加拿大及一些欧洲国家已经不再将其用作疫苗防腐。

小罗伯特·肯尼迪发表硫柳汞（一种含有有机水银的疫苗防腐剂）可能和自闭症有关。他分析了水银中毒和自闭症的病征相似之处，也表示安曼教派儿童没有接受防疫注射，自闭症发病率很低。此研究没有任何流行病学数据支持。可是，美国疾病控制与预防中心回应此研究，指硫柳汞不似是自闭症的原因。但基于公众忧虑，疾病管制中心、食物及药物管理局，及国家健康署共同于一九九九年发表声明，要求药厂停止使用硫柳汞作为儿童疫苗防腐之用，但在成人疫苗中还有使用。

Thiomersal (INN), commonly known in the U.S. as thimerosal, is an organomercury compound. This compound is a well established antiseptic and antifungal agent.

The pharmaceutical corporation Eli Lilly and Company gave thiomersal the trade name Merthiolate. It has been used as a preservative in vaccines, immunoglobulin preparations, skin test antigens, antivenins, ophthalmic and nasal products, and tattoo inks. Its use as a vaccine preservative was controversial, and it was phased out from routine childhood vaccines in the European Union, and a few other countries in response to popular fears. The current scientific consensus is that no convincing scientific evidence supports these fears.