The move will take effect on December 8th.
The additional service will be operated by an Airbus A320 configured with eight seats in business and 150 in economy.
Robin Kamark, chief commercial officer, Etihad Aviation Group, said: “The introduction of the new fourth daily service to Riyadh is demonstrative of our commitment to the Saudi market, and of the increase in demand on this core route.
“This has been boosted by warm relationship enjoyed by the United Arab Emirates and the Kingdom of Saudi Arabia, and by the recent easing of entry visa regulations for tourists entering the Kingdom.
“Riyadh is a key market on our global network, and the additional service adds yet more attractive timings to both business and leisure travellers flying between both capitals, as well as more options for travellers connecting through Abu Dhabi onto Etihad’s global network.
“As Etihad and Saudia continue to strengthen their partnership, the new flight will also provide convenient travel options to our customers, allowing increased codeshare connectivity on joint services.”
Etihad Airways has a codeshare agreement in place with Saudia.
The two airlines place their flight codes on each other’s services between Abu Dhabi and the Saudi Arabian cities of Dammam, Jeddah, Riyadh and Medina.
Etihad also places its ‘EY’ code on Saudia flights to Peshawar, Multan, Port Sudan and Vienna, while Saudia also places its ‘SV’ code to Etihad flights between Abu Dhabi and Ahmedabad, Belgrade, Brisbane, Chengdu, Chicago, Dusseldorf, Lagos, Melbourne, Moscow-Domodedovo, Rabat, Seychelles and Sydney.
Subject to regulatory approvals, Saudia will progressively add its code to Etihad flights between Abu Dhabi and 11 more destinations in nine countries including Amsterdam, Baku, Brussels, Dublin, Hong Kong, Kathmandu, Bangkok, Phuket, Nagoya, Tokyo and Seoul.