硫氧还蛋白还原酶（英语：thioredoxin reductase），缩写为TrxR或者TR，是一种NADPH依赖的包含FAD结构域的还原酶，活性形式通常为二聚体，属于吡啶核苷酸-二硫化物氧化还原酶家族。顾名思义，硫氧还蛋白还原酶是用来还原它的生理底物硫氧化蛋白的酶。它和硫氧还蛋白（Trx）、NADPH共同构成了硫氧还蛋白系统（Trx system）。哺乳动物体系的硫氧还蛋白还原酶属于硒蛋白。硫氧还蛋白还原酶有很多生物学功能，与人类某些疾病发病机制密切相关，目前在癌症研究中亦作为重要的抗癌靶点，受到广泛关注和深入研究。

Thioredoxin reductases (TR, TrxR) (EC1.8.1.9) are the only known enzymes to reduce thioredoxin (Trx). Two classes of thioredoxin reductase have been identified: one class in bacteria and some eukaryotes and one in animals. Both classes are flavoproteins which function as homodimers. Each monomer contains a FAD prosthetic group, a NADPH binding domain, and an active site containing a redox-active disulfide bond.