| Adrien Loir | |
| Birth Date: | 15 December 1862 |
| Birth Place: | Lyon |
| Death Date: | 1941 (aged 78–79) |
| Nationality: | French |
| Field: | bacteriology |
| Work Institutions: | Pasteur Institute |
Adrien Loir (15 December 1862 - 1941) was a French bacteriologist born in Lyon. He was a nephew of Louis Pasteur, and for much of his career was associated with the Pasteur Institute.
From 1882 to 1888 Loir was an assistant in Pasteur's laboratory in Paris, where he performed research of swine fever. In 1886, he installed the first anti-rabies clinic in Saint Petersburg. Between 1888 and 1893 he made two journeys to Australia to conduct research of anthrax and pleuropneumonia. While there, he investigated the use of chicken cholera bacillus in an attempt to eradicate the country's rabbit infestation.
In 1893 he founded the Pasteur Institute of Tunisia, and for several years was a professor of hygiene and bacteriology at the colonial school in Tunis. In 1906 he traveled to Canada, where he demonstrated that the equine disease, dourine is caused by the parasite trypanosoma equiperdum.