Experiments were carried out to investigate the effect of the layer depth ratio on the mixing process of a two-layer stratified fluid in a laterally heated enclosure. Due to the lateral heating of the enclosure, a circulating convective flow is induced in each layer. The experiments were carried out in a box with inner dimensions of 10 x 10 x 10 cm(3). Two sidewalls of the box were made of stainless steel and served as heat exchangers, and the two other sidewalls were made of optical glass to facilitate flow visualization. The results show that when one layer is deeper than the other, the mixing time is reduced compared to its value in the case of equal-depth layers. When the top layer is deeper, the mixing times are generally larger than those for a deeper bottom layer. This indicates on an asymmetry in the system.