The deal, agreed by nearly 200 nations, keeps the protocol alive as the only legally binding plan for combating global warming. However, it only covers developed nations whose share of world greenhouse gas emissions is less than 15%.
The US - a major polluter - has never ratified the original 1997 protocol. The agreement had been due to expire later this year. The 12-day meeting in Qatar's capital Doha overran by more than 24 hours because of differences over whether rich nations should have to compensate poorer states for losses due to climate change.
The deal was finally agreed on Saturday after the 27-member European Union, Australia and several other industrialised nations signed up for binding CO2 cuts by 2020, AFP says. The protocol, however excludes some major polluters, including the US, China and India.
The gathering in Doha had also focused on a plan to adopt a wider treaty in 2015 that would apply to all countries and eventually replace the Kyoto Protocol.