ALQST, a London-based human rights group, identified the detainees released Thursday as Hatoon al-Fassi, Amal al-Harbi, Maysaa al-Manea and Abeer Namankani. Three other women who are defendants in the same trial were released in March.
The fate of several other female activists and male supporters who have been detained remains unclear.
Many of the women said they were tortured while in custody — an allegation that shocked many Saudis and intensified international criticism of the Saudi leadership. Saudi authorities have denied torturing prisoners.
The prominence of some of the detainees has also sparked outrage. In a March letter protesting the arrest of Fassi, a professor of women’s history, the Middle East Studies Association of North America noted that she was a “renowned historian of pre-Islamic Arabia” who was “widely respected internationally by her colleagues and the many younger scholars she has mentored.” Her arrest, the letter added, was a “travesty of justice.”