Jacob Georg Agardh (8 December 1813 in Lund, Sweden – 7 January 1901 in Lund, Sweden) was a Swedish botanist, phycologist, and taxonomist.
He was the son of Carl Adolph Agardh, and from 1854 until 1879 was professor of botany at Lund University. Agardh designed the current 1862 blueprints for the botanical garden Botaniska trädgården in Lund.
In 1849, he was elected a member of the Royal Swedish Academy of Sciences. Agardh was elected a Foreign Honorary Member of the American Academy of Arts and Sciences in 1878.
His principal work, Species, Genera et Ordines Algarum (4 vols., Lund, 1848–63), was a standard authority.