次黄嘌呤（英语：Hypoxanthine）也称「6-羟基嘌呤」，是一种天然存在的嘌呤衍生物。它的核苷酸肌苷酸是核酸的嘌呤核苷酸的合成前体。

黄嘌呤是次黄嘌呤被黄嘌呤氧化酶氧化的产物之一。在核苷酸合成中，次黄嘌呤在次黄嘌呤-鸟嘌呤磷酸核糖转移酶的作用下，转变为肌苷酸（IMP），可用于IMP的补救合成。

次黄嘌呤也是腺嘌呤发生自发脱氨的产物之一。由于它与鸟嘌呤在结构上十分相似，因此腺嘌呤的自发脱氨可导致DNA转录／复制出现错误。

Hypoxanthine is a naturally occurring purine derivative. It is occasionally found as a constituent of nucleic acids, where it is present in the anticodon of tRNA in the form of its nucleoside inosine. It has a tautomer known as 6-hydroxypurine. Hypoxanthine is a necessary additive in certain cell, bacteria, and parasite cultures as a substrate and nitrogen source. For example, it is commonly a required reagent in malaria parasite cultures, since Plasmodium falciparum requires a source of hypoxanthine for nucleic acid synthesis and energy metabolism.