Saudi Arabia's King Abdullah has appointed women to a fifth of the seats in the Shura Council, which advises the government on new legislation, state media said on Friday.
The king said in 2011 that women would join the unelected 150-member body, which functions like a parliament but without formal powers. He did not then specify how many would serve.
The council has had 12 women "advisers" since 2006, but women still have little role in public life in the religiously conservative kingdom, the birthplace of Islam.
In two royal decrees on Friday, King Abdullah reconstituted the council for a new four-year term and ordered that women should always hold at least 20 percent of the seats.
The ruling al-Saud family controls most top government posts the world's top oil exporter. The king appoints the cabinet. The only elections are for municipal councils that wield little power.
The Shura Council, composed mostly of academics, clerics, businessmen and former civil servants, vets legislation, recommending changes or additions to the government.
In his 2011 decree, King Abdullah also said women would be able to vote and stand for office in the municipal polls.
Women in the kingdom cannot travel, work or open a bank account without the permission of a male relative, known as their "guardian", and are barred from driving. Their testimony counts for less than that of a man in a court of law.
Liberals in the Gulf Arab state say Abdullah, who became king in 2005 after effectively ruling as crown prince for a decade before that, has pushed for modest social change, calling for women to have more opportunities to work.
Powerful conservative Sunni Muslim clerics have sometimes argued against allowing women a role in politics.
To comply with the kingdom's rigorous policy of gender segregation, the Shura council building must now be altered to include a separate entrance for women, the decree said.