The Independent Election Commission (IEC) last month ordered that the nine MPs be replaced, after almost a year of street protests and controversy over last September's fraud-tainted parliamentary polls.
While nine was far lower than other figures previously floated, a special tribunal said in June it should be 62, a quarter of all lawmakers, the ruling still prompted fury among many politicians.
Mohammad Rafiq Shaheer, a lawmaker from the western province of Herat, told AFP by telephone on Saturday: "We are outside the Parliament, the security officials are not allowing us to enter the parliament, and around 120 MPs... have also stood with us to support us."
Saturday's session opened with "new" MPs replacing those thrown out by the IEC, a parliament official said.
Among the replacement lawmakers was Ahmad Khan, a powerful warlord from northern Samangan province, who confirmed to AFP that he had taken his seat.
Ahmad Behzad, the second deputy speaker of the house and a member of the main group opposing President Hamid Karzai, condemned what he called an act of "treachery against the parliament".
The IEC was assigned by President Hamid Karzai to make the final ruling in the nearly year-long row over election disputes.
But the issue is highly controversial in Afghanistan and has prompted a string of angry protests on the streets of Kabul by supporters of rival politicians in recent months.
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