Frank Ellsworth Blaisdell, Sr. (13 March 1862 – 16 July 1946) was an American professor of surgery who also was a keen naturalist and collector who specialized in beetles, and contributed to the systematics of the Tenebrionidae and the Melyridae.
He joined Cooper Medical College in 1887 and graduated in 1889 to begin practice in San Diego.
During this period he married Ella Katherine Peek and they had a son, a namesake who went on to study radiology.
In 1910, Cooper College became affiliated to Stanford University and Blaisdell was appointed Professor of Surgery.
A part of his large collection of beetles, particularly tenebrionids, was destroyed in the 1906 San Francisco earthquake and fire, but the remainder are now in the California Academy of Sciences.