The Pope's popularity is down to where it stood in 2013, when he was elected leader of the 1.2 billion-member Roman Catholic Church, according to a Gallup poll.
The Pontiff's overall approval ratings among a random sampling of US adults slid to 59 per cent from 76 per cent early last year.
Favourable ratings among Catholic conservatives dropped from 72 to 45 per cent.
Gallup said the fall might be because US conservatives are turned off by the Pope's progressive stance on issues such as climate change and income equality - "issues that are at odds with many conservatives' beliefs".
