This thesis discusses the effectiveness of cultural diplomacy carried out by Japan and Indonesia. Indonesia and Japan have a history that was not good in the past, because Japan once colonized Indonesia and left bad memories in the minds of Indonesian citizens. but after World War II, Japan tried to improve their image from a colonial state to a peace- loving country. In 1958 Japan and Indonesia signed a peace agreement and since then they have collaborated in various fields such as economics, politics and social culture. The research in this paper uses qualitative methods and collecting data through literature studies and then supplemented with data taken from various sources such as the internet and media both print and online. Data collection in this paper is obtained from documentation. Analysis of qualitative data is carried out through three stages, namely data reduction, data presentation, and conclusion. JKT48 is a bridge of friendship between Indonesia and Japan as well as an instrument of cultural diplomacy and effective nation branding because it is a form of popular culture that is easily accepted by various elements of society. The success of cultural diplomacy and nation branding carried out by the two countries will impact on the emergence of interdependent relations between countries because of identical national interests.