孢子（英语：Spore，汉语拼音：bāo-zǐ）是一种脱离亲本后能发育成新个体的单细胞或少数细胞的繁殖体。

孢子一般有休眠作用，能在恶劣的环境下保持自有的传播能力，并再在有利条件之下才直接发育成新个体。孢子一般都是微小的单细胞。由于它的性状不同，发生过程和结构的差异而有种种名称。

生物通过无性生殖产生的孢子叫「无性孢子」，如分生孢子、孢囊孢子、游动孢子等；反之，通过有性繁殖产生的孢子叫「有性孢子」，如接合孢子、卵孢子、子囊孢子、担孢子等。在不同的生物的生活环之内，如植物、藻类、真菌和一些原生动物，孢子都担当着衍生下一代的角色。大部分的藻类减数分裂是在孢子形成时进行。

In biology, a spore is a unit of ****ual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavorable conditions. By contrast, gametes are units of sexual reproduction. Spores form part of the life cycles of many plants, algae, fungi and protozoa. Bacterial spores are not part of a sexual cycle but are resistant structures used for survival under unfavourable conditions. Myxozoan spores release amoebulae into their hosts for parasitic infection, but also reproduce within the hosts through the pairing of two nuclei within the plasmodium, which develops from the amoebula.