Mahjong Cop Ryū is a combination of a Japanese-style adventure game and a 1-vs-1 mahjong game. It is a direct sequel to the coin-op strip mahjong game Sukeban Janshi Ryūko, and picks up the story directly after the destruction of the Janrōkai, an evil mahjong-playing organization. The player takes the role of an investigator named Ryū who is looking to find the true nature of an even greater threat that has taken the Janrōkai's place.
The main story mode features extended dialogue sequences, but these are largely linear and the only options are "speak", "show", and "threaten". In order to proceed with the story, the player must defeat a variety of colorful opponents at mahjong. The actual mahjong play is largely traditional, though there are several special techniques the player can use to gain an advantage.
In addition to the story mode, there is also a free battle mode, as well as a mahjong quiz mode and several options to change the rules of the game.