In this proposal we want to study the evolution of the antiferromagnetic (AFM) order of CePt3Si in high magnetic fields up to paramagnetic phase boundary at ~ 25 T. Non-centrosymmetric CePt3Si exhibits not only unconventional superconductivity, but does also show unusual AFM order with k=(0 0 1/2). Surprisingly, instead of the expected slight decrease the AFM intensity substantially increases up to the highest field of 6.6T for H||[001]. Owing to its acentric structure, the magnetic order in CePt3Si is modified by spin-orbit couplings resulting in antisymmetric Dzyaloshinskii-Moriya (DM) exchange, which may originate in complex AFM state with a oscillating weak ferromagnetic mode, and rich magnetic phase diagrams. The corresponding distinctive magnetization processes can identify the role of DM-interactions. With the proposed experiment we want to test the hypothesis of whether chiral modulated spiral magnetism exists in CePt3Si by following the AFM order to high magnetic fields.