The RDP, which broke away from the ruling party in 2007, took eight seats.
Election results rejected
Earlier on Friday, the RDP and seven other opposition parties rejected the results of the elections and said they would file a court challenge.
The parties instructed their legal teams to institute proceedings against the Electoral Commission of Namibia "for contravening the electoral law of the country," they said.
While African observers of the elections have pronounced them free and fair, opposition parties also complained about not being adequately informed about the vote verification process.
Hifikepunye Pohamba, Namibia's re-elected president, has been in power since 2005 but his Swapo party has maintained a majority of seats in parliament since the country received its independence from South Africa in 1990.
Namibia has enjoyed political stability and economic growth, but is struggling in the face of rising poverty, unemployment and widening cracks in its once highly regarded health care and school systems, further exacerbated by the global recession.