"I have taken the decision to close the border with Colombia for 72 hours," the leftist leader said in a nationally televised address, calling it a "hard" but "inevitable" choice.
The closure came a day after Maduro signed an emergency decree removing Venezuela's largest bank note, the 100 bolivar bill, from circulation because of what he called a Washington-sponsored plot against his country's troubled economy.
Maduro said a Venezuelan investigation had found that billions of bolivars, in bills of 100, were stashed away by international mafias, mainly in Colombian cities but also in Brazil.
He said Venezuela was the victim of a plot to "destabilize" the economy led by a group "contracted by the US Department of Treasury."
Speaking Monday, Maduro said Venezuelan authorities had seized 64 million bolivars ($96,000, at the highest official exchange rate) from people trying to sneak them back into the country.
He called for talks with his Colombian counterpart, Juan Manuel Santos.
Pummeled by low oil prices, Venezuela is mired in economic crisis and crippled with the world's highest inflation rate -- set to hit 475 percent this year, according to an IMF forecast.
The 100 bolivar bill is worth fewer than three US cents at current market rates.
Venezuelans have to carry around huge stacks of them even for small purchases.
Maduro has closed his country's border with Colombia in the past in times of crisis.
Last year, facing the socialist party's looming defeat in legislative elections, he closed it after alleging Colombia-based paramilitaries had attacked a Venezuelan anti-smuggling patrol.
Tens of thousands of Colombians living in Venezuela were deported or fled in fear of reprisals.