Their exit comes after they defended their double scull gold medal at the Beijing Olympics.
Caroline and Georgina won the first of their double scull world titles in Seville, Spain, in 2002 and retained it in 2003 in Milan, Italy, before capturing their first Olympic title at Athens in 2004.
They were world champions again in 2005 in Gifu, Japan.
Caroline and Georgina now plan to take some time out while they decide their futures off the water. "Retiring now just feels right," Caroline said.
"It's been a great time in our lives and we couldn't have done it without (coach) Richard (Tonks).
"We have always said they should give out three medals not two."
Georgina said there was life in New Zealand rowing after them.
"There are many young athletes coming up through the ranks and some are already junior and under-23 world champions.
"Rowing has a wealth of talent and the sport is very healthy. It's a great time to bring on the young talent and for us to say good bye."
The Hawke's Bay twins have been international rowers for almost a decade.
Their victory in Beijing was one of the closest in the history of the Olympic Games and their second gold medal put them into an exclusive club of New Zealand Olympians who have successfully defended their titles.
After difficult seasons in 2006 and 2007 -- when they still won a world bronze and a world silver medal -- they entered 2008 as outsiders to retain their Olympic title in Beijing.
But they pulled through to beat Germany in a thrilling final, coming from behind to snatch victory by one hundredth of a second.
This was the first time that the Olympic women's double scull title had successfully been defended.
"The twins are an example of guts and determination that every young athlete can look up to," said Tonks, their coach of eight years.
"They have delivered when it has mattered most and no coach could ever ask for more. "It's been a pleasure to work with them."
Rowing NZ chairman Bill Falconer said the sport would be "forever indebted" to the twins.
"They are icons not only in New Zealand but in world rowing and world sport.
"It's always a tough decision to retire but these girls have given a decade of their lives to winning and they are leaving the sport as Olympic champions. They have been, and will remain, inspirational."
