基因毒性（英语：Genotoxicity）是指会破坏细胞内遗传物质完整性的性质。如六价铬、苯、芳香胺都是具有基因毒性的化合物。游离辐射也具有基因毒性。

基因毒性的物质由于会造成基因突变，帮助肿瘤的成长，常被视为潜在的突变原及致癌物质。以芳香胺为例，因为具有亲核性，可以和DNA产生的共价键，形成芳香胺及DNA的加合物，无法准确的复制基因，因此也认为是突变原之一。

若精子或卵子受到基因毒性物质影响，其基因发生变化，且基因的变化会传递到未接触基因毒性物质的后代。

In genetics, genotoxicity describes the property of chemical agents that damages the genetic information within a cell causing mutations, which may lead to cancer. While genotoxicity is often confused with mutagenicity, all mutagens are genotoxic, whereas not all genotoxic substances are mutagenic. The alteration can have direct or indirect effects on the DNA: the induction of mutations, mistimed event activation, and direct DNA damage leading to mutations. The permanent, heritable changes can affect either somatic cells of the organism or germ cells to be passed on to future generations. Cells prevent expression of the genotoxic mutation by either DNA repair or apoptosis; however, the damage may not always be fixed leading to mutagenesis.