USADA, who exposed the seven-times Tour de France winner as a drug cheat, said in a statement that Armstrong's admission to a worldwide television audience was a good first step but that the 41-year-old needed to do more.
"Tonight, Lance Armstrong finally acknowledged that his cycling career was built on a powerful combination of doping and deceit," said USADA chief Travis Tygart in a statement released shortly after the gripping 90-minute interview.
"His admission that he doped throughout his career is a small step in the right direction.
"But if he is sincere in his desire to correct his past mistakes, he will testify under oath about the full extent of his doping activities."
Armstrong, who has been stripped of his seven Tour wins and a bronze medal from the 2000 Sydney Olympics, took Winfrey's quick-fire, probing questions head on, owning up to the type of drug use that has tainted the sport he said he loves.
With cycling reeling from doping scandals and its place at the Olympics said to be under threat, Armstrong said he would do what he could, if called upon, to help rebuild its tattered image.
"I love cycling and I say that knowing that people see me as someone who disrespected the sport, the colour yellow," Armstrong told Winfrey.
"If we can, and I stand on no moral platform here, if there was a truth and reconciliation commission, and I can't call for that, if they have it and I'm invited I'll be first man through the door."
The World Anti-Doping Agency also called on Armstrong this week to reveal under oath what he knows about doping in cycling.