Sergio "Serge" de la Rama Osmeña III (Tagalog pronunciation: [ˈsɛɾdʒ ʔosˈmɛɲa]; born December 13, 1943) is a Filipino politician and legislator who served as a Senator of the Philippines.

In his eighteen years in the Senate, Osmeña chaired the most committees and filed the most bills in the history of the institution.

In November 1974, he embarked on a hunger strike along with his cellmate, Eugenio "Geny" Lopez, Jr., to protest the unjust detention of thousands of innocent Filipinos.

After the removal of Marcos, Osmeña returned to the Philippines and held positions in business and government corporations in the 1990s: He served as Secretary General of the Progressive Party cluster NUCD-UMDP from 1991 to 1992.

In 1995, Osmeña was invited by President Fidel Ramos to join in the senatorial race under the Lakas-Laban ticket.

The Senate offices and session hall were transferred to the GSIS Building at the Financial Center in Pasay.

As Chair, Osmeña tried to block the approval of the construction of the Casecnan and the San Roque dams having discovered gross discrepancies in the costs and benefits of the projects.

It was Osmeña who pointed out that the government would be investing a ridiculous amount of more than P385,000 to irrigate an additional hectare of rice paddy.

In 2001, Osmeña was one of the senators who voted in favor of opening the second bank envelope for the impeachment case filed against Joseph Estrada.

While serving his initial term as senator he held a concurrent position as board director of San Miguel Brewery (HK), Ltd.

Serge Osmeña is a farmer and businessman by training and was educated at Harvard, Georgetown, and the University of the Philippines.