Researchers investigating the ancient Kitora tomb in Asuka, Nara Prefecture, said Tuesday that paintings on the walls of the stone chamber remain intact.
The last time their condition was checked was during a probe in 2001.
The research team said that using a remote-control digital camera, they checked the condition of the chamber's plastered and painted walls and found no mold in the stone chamber.
Parts of the walls have appeared close to coming off since their discovery via a fiberscope camera probe in 1983. Researchers say it is vital to begin restoration work soon.
The tomb dates from the late seventh to early eighth centuries.
On Wednesday, the researchers plan to start digging a passage alongside a grave robber's tunnel leading to the chamber, a step necessary for repair work.
After finishing the digging in early February, they intend to take a direct look at the inside of the chamber through a hole and then excavate the chamber in April at the earliest.
The research team, mostly made up of members of the National Research Institute for Cultural Properties, will then make plans for maintenance and restoration.
The Kitora tomb is about 14 meters in diameter and 2.6 meters in height. The walls of the stone chamber have been confirmed to have paintings of the four gods of ancient Chinese mythology.
It is thought that someone related to Emperor Temmu of the seventh century lies in the tomb.
