The spatial and temporal distributions of the mixed layer depth (MLD) in the North Pacific were examined using the Argo float data for 2000--2003. The MLD distributions generally corresponded to those obtained from the WOA01 except in the northwestern Pacific (30¿--45¿N, 140¿E--170¿W), where the MLDs detected by the floats were systematically shallower (deeper) in the region to the north (south) of the Kuroshio Extension (KE) than the climatological MLDs. This region was also characterized by considerable mesoscale variability in the spatial distribution of the MLD. A detailed examination of the seasonal evolution of MLD in selected small areas revealed that both the timing and amplitude of the seasonal changes obtained from the Argo floats differed remarkably from the climatology in the south of the KE.