We examine the effects of self-construal and social support in friendships on loneliness using data from a random sample of residents in Tokyo, Japan. We find that the relationship between interdependent and independent self-construal is not orthogonal, as found by studies in the West, but moderately positive. Net of independence, interdependence significantly and positively predicts perceived social support, but not vice versa. By comparison, neither interdependence nor independence completely absorbs the protective effect of the other on loneliness. Our full models including other variables (e.g. gender, age, and extraversion personality) show that interdependence matters more in explaining perceived social support and loneliness. Moreover, perceived social support partially mediates the negative effect of interdependence on loneliness. We discuss implications of these and other related findings for future research on self-construal and subjective wellbeing across societies.