The two countries announced the border would be unlocked last week after a thaw in relations that included a visit to Bangkok by Burma's foreign minister.
Crowds of people gathered to cross the border on Tuesday morning as Burmese soldiers removed the wire barricades blocking the Thailand-Myanmar Friendship Bridge - one of the countries' major checkpoints.
Burma closed its border with Thailand on 22 May after the Thai army fired shells into Burma during a battle between the Burmese army and ethnic Shan rebels.
Thailand said its forces opened fire only when the fighting spilled over the border, but Burma accused them of trying to aid the rebels.
Tensions eased
"The reopening of the border checkpoints illustrates that the close relationship between the two countries has returned," Thai Prime Minister Thaksin Shinawatra told reporters.
Boomthiem Chokewattana, head of the customs office at Mae Sot - one of the main border crossings - said the border closure had lost Thailand about 5 billion baht ($113.7 million) in trade.
Another product of the porous 1,800-km (1,125-mile) border is drug running.
Thai Foreign Minister Surakiart Sathirathai said after his talks with his Burmese counterpart Win Aung two weeks ago that they two sides had discussed co-operating in the fight against illegal drugs.
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