In recent years, the Vietnam people residing in Japan have constantly increased. Together with many foreign communities living in Japan, Vietnamese expatriates are contributing to build a Japanese society diversity of language and culture. Profoundly, Vietnamese people manage to maintain Vietnamese language while they still have to adapt to the full specification of rules in Japan society. The article analyzes the effort to maintain mother tongue of Vietnam families in Japan with the aim to foster research of Vietnam community in foreign countries, as well as informing efforts of Vietnamese expatriates pay tribute to their origin in the world.