Ruling that the plaintiffs did not provide sufficient proof of alleged involvement on Wednesday, district court Judge Richard Conway Casey cleared numerous leading Saudi officials and financial institutions of any wrong-doing.
Reacting to the 62-page ruling, Prince Bandar bin Sultan - Saudi Arabia's ambassador to Washington - welcomed the judge's stance, which he said was "consistent" with the findings of the US 9/11 commission.
"The decision of the court is consistent with the findings of the 9/11 commission, which concluded after exhaustive investigation that there is no evidence of involvement in or financial support for terrorism by the Saudi government or the royal family," the prince said.
The plaintiffs - including relatives and insurers of victims of the 2001 attacks - had taken about 200 people and institutions to court.
Specific charges included providing material support to the planners of the deadly attacks on New York's twin World Trade Center towers and the Pentagon, outside Washington, which killed 2700 people.
The suits blamed Usama bin Ladin, al-Qaida, Saudi leaders, several financial institutions and some charities.
Casey ruled that the plaintiffs did not have sufficient evidence to pursue a case against Saudi Arabia, Prince Muhammad al-Faisal al-Saud, Defence Minister Prince Sultan Ibn Abd al-Aziz al-Saud and Prince Turki al-Faisal, the Saudi ambassador to London.
More cases dropped
"In the aftermath of 9/11, the Kingdom of Saudi Arabia has been confronted with many false charges.
"As the real facts emerge, we hope we can all move forward in the spirit of cooperation and mutual support, which is so critical to winning the war on terrorism," bin Sultan added.
Casey also rejected charges against banks such as Al-Rahji Bank, the Saudi American Bank and the Arab Bank.
However, the judge permitted cases to be brought against bin Ladin's family construction firm, the Saudi Bin Ladin Group; the National Commercial Bank; and charities including the Muslim World League.