We demonstrated in situ observation of the swelling of stratum corneum (SC) by cantilever-assisted two-beam interference microscopy (CATBIM) in this study. The CATBIM enabled us to observe the refractive index changes of the small region of a stratum corneum in 1% glycerin solution. Interference pattern images of the SC were successfully acquired. The fringe interval was almost the same during the experiments. On the other hand, the thickness by swelling of the SC increased with time. The speeds of swelling decreased with time.