Ivory Coast's new senate took office on Thursday, defying opposition protests that the assembly was a costly rubber stamp for President Alassane Ouattara.
Sixty-six senators were elected on March 24, delivering a massive majority for the ruling RHDP party. Thirty-three others are due to be appointed by Ouattara himself.
The senate is the fruit of a revised constitution overwhelmingly approved by a referendum in 2016 - the cornerpiece of Ouattara's strategy of change since coming to power after a bloody five-month crisis in 2010-11.
He ousted the then-president, Laurent Gbagbo, who refused to step down after losing elections and is now on trial in The Hague for war crimes.
Violence between supporters of the two rivals claimed about 3 000 lives.
Jeannot Ahousso-Kouadio, 67, currently secretary of state in charge of political dialogue, was unanimously elected senate president, minus one abstention, in the inaugural session.
Fifty of the 66 seats were won by the RHDP on March 24 in a vote based on indirect suffrage, being held among municipal and regional councillors.
Ahousso-Kouadio said the new assembly would be vital for "taking into account the problems of people at the grassroots of society, since we come from community level".
The spokesperson of the centre-left opposition Ivorian Popular Front, Boubakar Kone, told AFP, "It's an illegal institution, gobbles up cash and goes against the interests of the country."
The senate is scheduled to begin its full programme on April 12.
The new constitution also created the post of vice president.
The opposition boycotted the referendum on the charter, deriding the proposed constitution as undemocratic and crafted to let Ouattara boost his grip on power and hand-pick his successor.
It is demanding an overhaul of the country's election watchdog, the Independent Electoral Commission, ahead of the next presidential vote, due in 2020.