In the case of laminar mixing in stirred tank, the mixing pattern formed is determined by the streakline originating from the tip of the impeller, and with time its profile approximates the shape of the streakline. An accurate understanding of the configuration of the streakline is therefore important in analysis of the mixing mechanism. In chaotic flow field where global mixing occurs, the fluid trajectory tends to expand exponentially in a particular direction, and it is therefore difficult experimentally to visualize a streak as a "line" because the streak behaves as a "sheet" that has helical envelope. In the present study, we have developed a novel technique to visualize distinct streaklines in a three-dimensional flow field. In this technique, the expansion of streaks is suppressed by the surface tension of surfactant molecules in the tracer fluid, thus allowing the visualization of distinct streaklines generated from the tip of the impeller blade in a stirred tank. This streakline can exist stably and remain in the form of a line for a long time, and there is little leakage of colored component due to the effect of molecular diffusion.