Bostock joined Asos in January after stepping down from her previous role at Marks & Spencer, where she was general merchandise executive director.
At Asos Bostock was charged with leading the 350 strong product and trading team as the company continues is aggressive international expansion and the addition of new lines, such as its Primark range.
The Asos board is considering whether Bostock’s role – which will be looked after by the current team in the interim – should be directly replaced.
Nick Robertson, Asos chief executive, says: “Kate and I have agreed that Asos is not the right platform for her talent. Of course we are disappointed that things haven’t worked out and Kate leaves with our very best wishes.”
Bostock, who has also held senior roles at George and Asda and Next, says Asos is a “formidable business” but adds: “Sadly, I’ve concluded that Asos isn’t the right place for me.”
Asos’ share price was up 0.04 per cent to £44.43 at the time of writing.