We investigate the deformation of involution and multiplication in a unital C^* -algebra when its norm is fixed. Our main result is to present all multiplications and involutions on a given C^* -algebra mathcal{A} under which mathcal{A} is still a C^* -algebra whereas we keep the norm unchanged. For each invertible element a in mathcal{A} we also introduce an involution and a multiplication making mathcal{A} into a C^* -algebra in which a becomes a positive element. Further, we give a necessary and sufficient condition for that the center of a unital C^* -algebra mathcal{A} is trivial.

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