White Coco opened its doors last month at 13 South Parade, previously occupied by Vanilla.
The brainchild of Sally Boddington, the shop offers a collection of ladies clothes with a balance between chic fashion and classic style.
The brand already has shops in Hungerford and on Kings Road, Chelsea.
The shop also sells gifts and homeware, with stock arriving every week.
Vanilla had been a fixture in Summertown since 2000, but closed in March after its owner, Renate Beaumont, retired.
Like its sister stores, the new Summertown shop will stock a handpicked range of clothing.
It will be open between 9am and 5.30 pm from Monday to Saturday, while it is closed on Sundays.