A mechanism for the formation of scattering centers in KDP crystals is reported. The crystals were grown from aqueous solution doped with a minute amount of sodium metaphosphate. From the observation using laser tomography, it was found that the density of the scatters rises with the increase of the concentration of the additive. The mother liquor macro inclusions also occur in the sector boundaries and pyramidal sectors when the dopant concentration is high enough. The scatters are proposed to be micro solution inclusions caused by the inhibition effect of metaphosphate on the growing faces.