The present invention relates to a water-purifying device for an aquarium including a lamination type filter container. According to the present invention, the water purifying device for an aquarium comprises: a water supply pipe for supplying contaminated water in an aquarium to a water purifying container； a bubble generating device for generating bubbles in the contaminated water supplied by the water supply pipe and floating foreign substances； and a water purifying container including a bubble removing pipe connected to the inner side of the water purifying container by being formed at the upper end of the water purifying container to remove foreign substances, in other words, bubbles formed by the bubble generating device. An ultraviolet ray sterilizing lamp is formed between the bubble removing pipe and the bubble generating device in the water purifying container. A microorganism carrier is included on one side of the water purifying container, and a filter unit in which multiple containers having a contaminated water outlet bored thereon are piled up, is installed on one side of the bottom. The contaminated water outlet formed on the container of the filter unit is piled to be connected to the adjacent contaminated water outlet, in a zigzag pattern. So, the contaminated water is discharged through a drain while being purified by passing from the container in the uppermost part to the container in the lowermost part in the longest distance. According to the present invention, the water-purifying device for an aquarium enables t the first purification and sterilization in the water-purifying container by removing contaminants by using bubbles to purify the contaminated water in the aquarium and sterilizing the water in the purifying container by using ultraviolet ray sterilization. Also, the water purifying device for an aquarium can maintain an optimal sterilization state and a purification state by enabling second sterilization by using the microorganism by
