The velocity field in a standard mixing reactor with a Rushton impeller is analyzed by using techniques from the theory of nonlinear dynamical systems. I is shown that the dynamical behavior contains a quasi-periodic motion with three frequencies, f(p), the frequency associated with the rotation of blades, f(p)/6, and a third frequency f’. Relying on an evaluation of the correlation dimension equal to 3.9, the phase space is likely to be at least four-dimensional. Moreover a set of four ordinary differential equations is indeed automatically obtained by using a global vector field reconstruction technique, confirming the existence of a 4-D-deterministic behavior contributing to the dynamics of the system.