Märta Margaretha af Ugglas (née Stenbeck; born 5 January 1939) is a Swedish former Moderate Party politician. She was Minister for Foreign Affairs between 1991 and 1994.
She is the daughter of Hugo Stenbeck, the founder of Investment AB Kinnevik, and the sister of Jan Stenbeck who took over that business from their father. She graduated from , and later married Bertil af Ugglas who became the Party Secretary of the Moderate Party. She fought a bitter feud with her brother over the family fortune, and subsequently withdrew from her brother and Kinnevik.
She was an editorial writer at Svenska Dagbladet for five years, and sat in the Swedish Riksdag between 1974 and 1995.
After the election victory in 1991, Margaretha af Ugglas became Sweden's second female Minister for Foreign Affairs. Her term included the finalisation of the negotiations leading up to Sweden's entry into the European Union.
In 1992, together with an EU Commissioner and nine other Ministers of Foreign Affairs from the Baltic Sea area, she founded the Council of the Baltic Sea States (CBSS) and the EuroFaculty.
The Moderate Party lost the 1994 election and she was elected to the European Parliament in 1995.
She is a former Chairman of the Jarl Hjalmarson Foundation.