The effect of the surfactant concentration on the terminal velocity, shape, and drag coefficient of freely rising bubbles in a non-Newtonian, pseudoplastic liquid was studied. It is known that surfactants affect the bubble terminal velocity by changing both the shape and surface mobility of the bubble. In this work we studied separately the effect of surfactants on the shape and surface mobility by using the recently obtained drag curves for freely rising bubbles with and without surface mobility. It was shown that, within the range of surfactant concentrations studied, the latter had no effect on the bubble shape. However, the effect on the bubble surface mobility was significant. It was shown that the transition from a bubble with an immobile surface to a bubble with a mobile one is a function of the surfactant concentration, terminal Reynolds number, and rheological properties of liquid. The values of these parameters at which transition occurs were determined.