"Fitch Ratings has affirmed Switzerland's long-term foreign and local currency Issuer Default Ratings (IDR) at 'AAA'," said the agency in a statement.
Fitch also held the country's short-term rating at 'F1+'.
The decision reflects the country's "advanced, diversified and wealthy economy," and a record of low and stable inflation, said Fitch.
Inflation was at minus one percent in May.
"The economy has sustained resilient growth despite the global financial crisis, rebounding quickly from a contraction in 2009," it said, while citing also well managed public finances and strong institutions.
Swiss government debt dropped last year to 36.5 percent of GDP compared to 54.9 in 2003, increasing the room for fiscal manoeuvre in the event of a severe economic downturn, the agency said.
It warned that "significant reforms" needed to be made to curb the effects of an ageing population on Switzerland's public finances however.