The decision was taken by decree in late November and posted on the Privy Council's website on Wednesday.
The announcement said the delay will allow the government "to consult widely with all stakeholders."
The delay comes just before Friday's commemoration of the 24th anniversary of the massacre at Montreal's Ecole polytechnique, Canada's worst mass shooting.
Fourteen women were killed during gunman Marc Lepine's rampage, which led to a call for stronger gun laws.
The rules would help keep Canada in compliance with international conventions on arms smuggling.
Some gun enthusiasts have objected to the regulations because they said they would increase costs for manufacturers, who would pass the increase on to gun buyers.
Jean-Christophe de Le Rue, a spokesman for Public Safety Minister Steven Blaney, said Thursday the government wants to take into consideration the concerns of hunters, farmers and sports shooters who obey gun laws.
"That's why the United Nations convention on marking firearms has been postponed for two consecutive years," he said. "We're not making any apologies about consulting Canadians on a common-sense approach, including possible repeal, which will keep Canadians safe without the bureaucracy."
Ontario Conservative MP Cheryl Gallant used her website to thank those who had supported the postponement.
She said she had asked for their support to put pressure on the government to delay the measure and had received hundreds of replies.
"Our government has heard us," she said.
The government noted in October 2012 that the repeal of the long-gun registry has created a gap in Canada's international obligations with regard to two protocols on arms smuggling.
The government posting of the measures in the Canada Gazette said that ensuring most firearms in Canada had unique serial numbers would meet some of the specifications of those international protocols.
The Conservative government, which scrapped the gun registry created in response to the Ecole polytechnique killings, has delayed the serial numbers measure at least four times.