Studies on the relationship of biculturalism and psychosocial outcomes are still in the fledgling stages. Given the limited attention to bicultural adult, the rationale behind the study is that bicultural individuals will be exposed to more demanding and novel situations, and thus, will possess more effective coping skills and interpersonal flexibility. The development of bicultural identity will not only entail the development of the intricacies of the individual's heritage culture, but the development of another cultural identity that may entail a vastly different culture. This study examined the relationship of biculturalism with cognitive-flexibility and self-efficacy of Japanese bilingual adults. Participants (n=210) were Japanese and English bilinguals ranging between 18 to 65 years old living in Japan or the US. All participants were alumni of international schools in Tokyo, Japan. While biculturalism was operationalized by modeling after the abbreviated multidimensional acculturation scale, an exploratory factorial analysis was performed to find the best item loadings to create a composite variable that represented biculturalism. Numbers of years working in Japan and in the US were unique independent variables used in this study. The findings points to a positive moderate correlation of biculturalism with cognitive-flexibility and self-efficacy. A linear multiple regression analysis was conducted and number of years working in the US was a strong predictor. A two-way ANOVA showed that individuals working more years in the US showed a significantly higher level of cognitive-flexibility and self-efficacy than individuals that worked less in the US. Lastly, individuals' perceptions of one's biculturalism and the substantive experiences were associated with cognitive-flexibility and self-efficacy. The implication of the study suggests that being able to navigate and function in Japan and the US may be related with the development of cognitive-flexibility and self-efficacy.