Adrien Loir (15 December 1862 – 1941) was a French bacteriologist born in Lyon.

From 1882 to 1888 Loir was an assistant in Pasteur's laboratory in Paris, where he performed research of swine fever.

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.