Police in Zurich said the couple, aged in their 70s, received a call in February from a woman posing as their granddaughter, claiming she was in financial difficulty.
Over the course of several weeks, she allegedly convinced the couple to hand over money to a friend of hers.
The couple only realised they had been scammed in mid-March, when they contacted their real granddaughter to ask why they had not heard back from her in a while, only to find out she had never asked them for money.
“This is certainly the biggest such case on record in Zurich, and perhaps in Switzerland,” Judith Hoedl, a Zurich police spokesman said.
She said these types of scams – where someone posing as family pretends to be in desperate need of money to trick elderly people out of their savings – have long been a problem in the Swiss financial capital.