Soft-elastic reactor (SER) has been demonstrated as an alternative approach to effective mixing of viscous liquid. Here, the mixing performance of Newtonian fluid—glycerin water solutions (1200±50 mPa•s) was experimentally investigated for the first time inside a simple cylindrical SER with soft-elastic baffle (SEB) aligned in parallel to the SER axis. Visualization based on an acid-base reaction was used to reveal the presence and the disappearance of isolated mixing regions. The mixing performance was characterized using the mixing curve and the mixing time. The effect of SEB positioning on mixing intensification was explored. Results show that a single SEB could improve mixing efficiency with the optimal positioning angle of 90°. With the increase of the number of the SEBs, the mixing efficiency was found to be improved regardless of positioning angles. Compared with the SER without SEB, adding a single SEB could reduce the mixing time by about 34% at the probe penetration depth of 2.5 cm and the penetration frequency of 1.0 Hz. Efficient mixing for SERs of large length to diameter ratios was also achieved with the presence of SEB.