Make-up artist Charlotte Tilbury was taskted with posting the video of Kate, which shows her on the beach in a black Huit bikini, facing not one, but six buckets of ice-cold water.
"Kate has asked me to upload her ice bucket challenge for her," Catherine captioned the image. "Please support ALS and raise money for this very worthy cause."
Before facing the water, Kate nominated actress Liv Tyler, Jack Nicholson and radio presenter Nick Grimshaw to face the challenge.
The Ice Bucket Challenge is all in aid of helping to raise awareness and money in support of ALS, also known as Lou Gehrig's disease and Motor Neurone Disease, a condition that attacks the spinal cord.
Other celebrities to have taken part include Victoria Beckham, Justin Bieber, Rose Huntington-Whiteley, Jennifer Lopez and James McAvoy.