The opening means that humanitarian aid can now reach the rebel-held northwestern parts of Syria. On Tuesday afternoon, a convoy of 17 trucks filled with supplies reportedly crossed the border crossing in Idlib.
Bab al-Hawa was closed in July due to a deadlock in the UN Security Council when it could not agree on a resolution. The passage provided about 85 percent of aid to the Idlib region.
According to the UN, there are more than four million people in northwestern Syria who are in need of water, medicine and other necessities of life.
Earlier this summer, Syria agreed to keep the Bab al-Salameh and al-Rai border crossings open from Turkey until November 13.