The epidermis of scales in the abdominal parts from freshwater- and seawater-adapted guppies(Poecilia reticulatus) were studied respectively by scanning- and transmission- electronmicroscope. In the seawater adapted group, the surface area of pavement cells is increased nearly twice as much as that of freshwater-adapted group, and the pavement cells are relatively flattened. Adaptatoin to seawater causes the increment of the density of glycocalyx in the surface of the microridge of pavement cells, as well as the well developed intercellular junctional complex(desmosome) between neighbouring filament-containing cells. Also, intercellular space between adjacent filament-containing cells is more frequently observed in the epidermis of seawater adapted guppy.