Calcium-Aluminium-rich inclusions (CArs) are the first solids to form in the early Solar System. They are oftensurrounded by Wark-Lovering (WL) rims, composed of sequential mineral layers, that offer a record of the conditions during the earliest stages of Solar System evolution, just after CAi formation. Analyses of oxygen and magnesium isotopes in nine CAIs and their WL rims selected in CO, CR, and CV chondrites, displaying different alteration histories, permit an investigation of the evolution of 0 isotope compositions in the early Solar System, and the processes that caused it.