Zharmakhan Tuyakbai announced the move at a press conference in Almaty today, saying that he was also giving up his membership in the party.
Tuyakbai said that he didn't want to have anything to do with the newly elected parliament but didn't articulate further his reasons for leaving the party.
Last week, Tuyakbai called the recent parliamentary elections "massive violations of voters' rights."
The elections were held on 19 September with a run-off election for 22 seats held on 3 October.
Otan, the party of Kazakh President Nursultan Nazarbaev, won 42 of the 77 seats in parliament, followed by the pro-presidential election bloc AIST which took 11 seats.
At the press conference today, Tuyakbai was asked how the move affects his relationship with President Nazarbaev. "I'm still in the president's team," he said. "I am waiting for President Nazarbaev to speak on the issues I have raised."
For more on the Kazakh elections, see RFE/RL's dedicated webpage "Kazakhstan Votes 2004."