Guilhermina Marçal (also known as Sister Guilhermina) is a humanitarian activist from Same, East Timor. She is the Provincial superior of the Canossian Sisters in East Timor. She was active in support for East Timor independence and would smuggle messages into prisoners. She was appointed, in 2010, to the Commission for the National Police of East Timor Promotion by the East Timor State Secretary for the Council of Ministers, Isabel da Costa Ferreira.