The survey of 100 mums was launched by personalised CD service MixPixie to coincide with Mother's Day on Sunday, March 18.
The Irish boyband beat the likes of Lionel Richie, ABBA, Rod Stewart, Whitney Houston and Michael Jackson in the poll.
MixPixie co-founder Buffie du Pon said: "We decided to do the survey to help guide our customers choose the right songs for their mums' personalised CDs.
"'You Raise Me Up' is the clear winner from eight million songs in total and has already been included on hundreds of Mother's Day orders".
Westlife are due to embark on their farewell tour from May, after confirming plans to split last year.
Manager Louis Walsh recently predicted that member Shane Filan will have a successful solo career once the band part ways.
> Westlife to split: Five career-defining songs - video
Watch the video for Westlife's 'You Raise Me Up' below: