Alberta's Wildrose party is still the Official Opposition.
Speaker Gene Zwozdesky sent a letter to both Wildrose and Alberta's Liberal parties confirming his decision.
Zwozdesky says incumbency was the key factor in his ruling.
A defection by former Wildrose leader Danielle Smith and eight other caucus members had left both Wildrose and the Liberals with five seats each.
Wildrose house leader Shayne Saskiw applauded the decision saying it strengthens democracy.
Saskiw says Wildrose received over 440,000 votes in the last election, which is a stronger mandate than the Liberals and the NDP.