In this study, we analyzed factors that influence mutual favorability in Japan and Korea. Japanese and Korean high-school students, university students, and adults were asked to answer a questionnaire consisting of various items considered to be factors that influence mutual favorability. The respondents number 1,278 Japanese and 908 Koreans. As a result of the analysis, nine factors were identified as statistically significant in forming mutual favorability. In particular, four factors, “area of interest”, “interest in people”, “experience of visiting”, and “information on the Internet” of each country are strongly related to the formation of mutual favorability. Although there are minor differences between age groups among both Japanese and Koreans, “liking” was influenced when respondents are interested in entertainment, leisure, lifestyle and people or when they find positive information on the Internet. However, some factors indicate differences such as, Korean sports in Japan, Japanese animation and games in Korea. On the other hand, if they had no interest in each other's country, people and language, the option “other than liking” was influenced among both Japanese and Korean respondents. The same response is seen among respondents with no experience of visiting the other country or when they find negative information about each other's country on the Internet.