In the present paper we study nonlinear dynamics of quantum quadratic operators (q.q.o) acting on the algebra of 2×2 matrices M 2 (C). First, we describe q.q.o. with Haar state as well as quadratic operators with the Kadison-Schwarz property. By means of such a description we provide an example of q.q.o. which is not the Kadision-Schwarz operator. Then we study stability of dynamics of q.q.o.