Wintertime oceanic surface mixed layer has been believed to deepen due to cooling and wind stirring. However, it is shown that in the latitudes of 20¿--30¿ in the world ocean, there are regions where wintertime oceanic surface mixed layer shoals. The mixed layer shoaling is mostly accompanied by sea surface temperature (SST) cooling from January to February (from July to August), and SST warming from February to March (from August to September) in the northern (southern) hemisphere ocean. Further studies on the evolution of the mixed layer in these areas are suggested as these shoaling phenomena cannot be explained by existing theories of oceanic mixed layer based on monthly surface flux data.