A vortex reactor represents an important class of equipment in chemical processing industries pertaining to crystallization and precipitation. They are characterized by the presence of a vortex generated due to rotation of a centrally placed impeller/magnetic needle at its center. The addition of reactants into the vortex leads to their mixing under forced vortex conditions. Estimation of mixing time in such reactors is essential for the proper design of reactors. In this work, we propose a novel technique to estimate the mixing time in a vortex reactor using an ultrasonic technique. As tracer is injected into the bulk liquid being stirred, there is a change in the speed of sound of the liquid in the vessel. This dynamic variation of sound velocity is acquired and analyzed to determine mixing time as well as the dynamics of mixing process of the tracer. A frequency of 40 Hz is achieved which leads to estimation of mixing dynamics with high time resolution. Validity of the proposed technique is ensured by comparing mixing time against that determined using a conventional dye based photographic technique. The proposed technique is thereafter used to determine mixing time and mixing dynamics under different operating (needle rotational speed and liquid head) and geometrical (needle and vessel diameter) conditions.