Vitter, known for his advocacy of conservative social issues, became embroiled in scandal when his phone number was found in the records of Deborah Jeanne Palfrey, the "D.C. Madam." Jeannette Maier, the "Canal Street Madam," then alleged that Vitter had been a customer in her New Orleans brothel in the 1990s.
The committee said Vitter's alleged misconduct occurred before he was elected to the Senate and did not directly involve his office, The Hill reported Thursday.
Vitter has not admitted using prostitutes, although he did say that he had committed a "very serious sin."
The committee dismissed the complaint by Citizens for Responsibility and Ethics in Washington without prejudice, saying it could be renewed if new evidence comes to light.
"The Senate Ethics Committee has once again done what it does best: nothing," said Naomi Seligman Steiner, deputy director and communications director of CREW.