The split is reported to be amicable with Hatherley planning to spend more time working on her solo projects - while original bandmembers Tim Wheeler, MARK HAMILTON and RICK McMURRAY will begin work on their sixth album later this year (06).
An official statement reads: "After nine years Ash and Charlotte Hatherley have mutually agreed to part company. The decision is completely amicable and they wish each other the very best for the future.
"Ash are returning to the studio later this year to make the follow up to 2004's MELTDOWN album. Charlotte is currently recording tracks for her second solo album which she plans to release in the autumn this year."
Ash were formed in 1992 before recruiting fourth member Hatherley in 1997.