生物合成（英语：Biosynthesis）是简单的物质在生物体内经过酶催化后转变为更复杂的物质的多步骤的过程。在生物合成过程中，简单的化合物通过化学反应，转换成其他化合物，或聚合形成大分子。这个过程通常在代谢途径中完成。生物合成有时候在单个细胞的细胞器内进行，而一些需要多种酶催化的合成会在多个细胞的细胞器中进行。生物合成的例子包括脂膜和核苷酸的合成。

生物合成的必要元素包括：先导化合物、化学能（如ATP）和包括辅酶（如NADH和NADPH）在内的催化酶。通过上述元素可以合成生物大分子的基本元素。 一些重要的生物大分子包括由氨基酸通过肽键连接而成的蛋白质和由核苷酸通过磷酸二酯键连接而成的DNA分子。

Biosynthesis (also called biogenesis or anabolism) is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined together to form macromolecules. This process often consists of metabolic pathways. Some of these biosynthetic pathways are located within a single cellular organelle, while others involve enzymes that are located within multiple cellular organelles. Examples of these biosynthetic pathways include the production of lipid membrane components and nucleotides.