Flanker Kolisi, who captained the Springboks to Rugby World Cup glory in November, and World Rugby Player of the Year Du Toit have committed their futures to the Cape Town-based Super Rugby side until 2021.
Steven Kitshoff, Bongi Mbonambi, Scarra Ntubeni, Frans Malherbe, Damian Willemse and Dillyn Leyds will also remain with the Stormers.
They finished bottom of the South African standings in 2019 and head coach John Dobson knows they must realise their potential after securing the services of such key men.