嗜碱性球或嗜碱性粒细胞（英语：basophil granulocyte、basophils）是一种最少见的粒细胞，约占循环系统中白血球的0.01%至0.3%。其名称来源为这种白血球是嗜碱性的，即它们可以被碱性的染料染上色，如图中所示。

嗜碱性球的细胞质中有许多大的颗粒，在显微镜下容易与细胞核混淆，但当尚未染色时细胞核就清晰可见且通常分成两叶。肥大细胞与嗜碱性球有许多相似之处，如两种细胞都存有组织胺，一种会在特殊情形下被刺激释放的化学物质。如同大多数的粒细胞，嗜碱性球在需要时可由血液进入组织中。

Basophil is a type of white blood cell. Basophils are the least common of the granulocytes, representing about 0.5 to 1% of circulating white blood cells. However, they are the largest type of granulocyte. They are responsible for inflammatory reactions during immune response, as well as in the formation of acute and chronic allergic diseases, including anaphylaxis, asthma, atopic dermatitis and hay fever. They can perform phagocytosis (cell eating), produce histamine and serotonin that induce inflammation, and heparin that prevents blood clotting.