Maria Mercedes Reinares y Arrastia-Tuason also known as Mercedes Tuason (born September 27, 1930) in Lubao, Pampanga, is a Philippine diplomat and ambassador to the Holy See.
An alumnus of Saint Scholastica's Catholic college in Manila, Tuason has served in the field of nutritional sciences and was appointed plenipotentiary to the Holy See in 2009.
In the Philippines, Tuason is particularly known as an advocate of the Holy Rosary devotion and her roles in many charitable organizations, namely the Red Cross foundation.
In May 2003 Pope John Paul II awarded Tuason the Magistral dame of the Sovereign Military Order of Malta.
In May 23, 2012, Pope Benedict XVI awarded Tuason the Grand Cross of Merit for the title Order of Pius IX due to her charitable works and diplomatic service to the Roman Catholic Church, a coveted title that was not granted to ladies until November 1993.
Currently, the Order of Pius IX is the third to the highest ranking order granted by the Pope through chivalry, the highest being the Supreme Order of Christ.
Tuason is also known for her pro-life activism and cooperation with the Archdiocese of Manila in challenging the legalization of abortion through the Reproductive Health Bill.
Tuason has fluency in writing and speaking in Tagalog, English, Spanish and Italian language and has partial fluency in the Hokkien dialect.