In a dirt disposal structure of an aquarium protein skimmer, a foam generating chamber formed in a container body is a porous bubble guide column having pores for interconnecting a dirt collection box with the foam generating chamber. Water in an aquarium tank is entered into the foam generating chamber by a liquid-gas mixing device to produce fine air bubbles. Since the air bubbles entered into the pores contain a very small amount of moisture, small protein or peptide dirt is discharged in a concentrated form. A dirt collection box collects concentrated small protein or peptide dirt with a small amount of water to prevent the dirt collection box from cleaning the dirt too frequently. The small protein or peptide dirt rises with the air bubbles from the pores to an outlet, and the continuously rising air bubbles can stop the dirt from returning into the aquarium tank.
