The Friendship Bridge, as it's known, goes across the Amu Darya river from the border town of Termez and a train carrying aid was the first important vehicle to cross it on Sunday.
The bridge is vital for cities like Maza-e-Sharif as it now means trucks can deliver aid in 40 minutes. Without it, it takes 10 days.
The bridge was shut in 1997 because of fighting between the Taleban and opposition forces.
On Saturday, thousands queued up impatiently to get supplies from the UN World Food Programme (WFP) who were handing out aid in Kabul in their biggest operation in the country ever.