先导化合物（lead compound）是一种具有药理学或生物学活性的化合物，可被用于开发新药，其化学结构可被进一步优化，以提高药力、选择性，改善药物动力学性质。通过高通量筛选（high-throughput screenings）可发现先导化合物，或通过天然物的次级代谢产物找到先导化合物。新发现的先导化合物也许存在某些缺陷，如活性不够高、化学结构不稳定、毒性较大、选择性不好、药物动力学性质不合理等，需要进行化学优化，将药性提高至足以进行生物试验或临床试验的程度，再进一步优化使之发展为理想的药物，这一过程称为先导化合物的优化。

A lead compound (i.e. a "leading" compound, not lead metal) in drug discovery is a chemical compound that has pharmacological or biological activity likely to be therapeutically useful, but may still have suboptimal structure that requires modification to fit better to the target. Its chemical structure is used as a starting point for chemical modifications in order to improve potency, selectivity, or pharmacokinetic parameters. Furthermore, newly invented pharmacologically active moieties may have poor druglikeness and may require chemical modification to become drug-like enough to be tested biologically or clinically.