Describing hard-left President Nicolas Maduro as "illegitimate", US President Donald Trump said the National Assembly, headed by Guaido, is "the only legitimate branch of government duly elected by the Venezuelan people."
The US' announcement came soon after 35-year-old Guaido declared himself interim president of Venezuela.
The people of Venezuela have courageously spoken out against Maduro and his regime, Trump said in a statement, adding that the US' will continue to use the full weight of its economic and diplomatic power to press for the restoration of democracy in Venezuela.
He also urged other governments to recognize Guaido as the Interim President of Venezuela.
"We continue to hold the illegitimate Maduro regime directly responsible for any threats it may pose to the safety of the Venezuelan people," Trump said.
Observing that the Venezuelan people have suffered long enough under Maduro's disastrous dictatorship, Secretary of State Mike Pompeo said the US will work closely with the legitimately elected National Assembly to facilitate the transition of Venezuela back to democracy and the rule of law, consistent with the Inter-American Democratic Charter.
Meanwhile, the head of the Organization of American States also recognised Venezuela's National Assembly leader as the country's acting president.
"Our congratulations to @jguaido as acting President of #Venezuela. You have all our recognition to launch the return of democracy to the country," OAS Secretary General Luis Almagro tweeted