Gangseodaemyo is located in Sammyo-ri Gangseo district in Nampo City. The tomb faces south and the chamber was built over ground. It is a single-chamber tomb composed of corridor and main chamber. The walls and ceiling corbel of the chamber were made with huge finely trimmed granite stones. The main chamber walls were built up by piling slabs and by cutting the top surfaces of the slabs in slant direction, the walls were designed to taper upwards.

Murals were painted immediately onto the surface of the stone walls and the theme is the Four Guardian Deities. The Deities on the main chamber walls are huge enough to cover the entire wall, having no background images. Especially the Black Tortoise and Serpent scene shows a high degree of artistic perfection, hence, attracting public attention since the time of initial research.

Considering that the tomb has a typical single-chamber tomb structure, that murals are mainly on the Four Guardian Deities, and that the expressional technique of the Four Guardian Deities has reached its peak, Gangseodaemyo is presumed to have been built in the late sixth century.