The present study relates a within-family variable, birth order positi
on, to acculturation among second and third generation Japanese Americ
ans. The study tests a general hypothesis that firstborn (including on
ly children) will be less assimilated to the dominant culture than the
ir siblings in families where the parents are trying to maintain their
identity with the culture of origin. This hypothesis was generally su
pported. Compared to laterborn Nisei, firstborn Nisei were less assimi
lated. For example, firstborn Nisei were more likely to live in Japane
se American neighborhoods, to use and learn Japanese language, to have
stronger Japanese family values, and to be Buddhist or Shinto. Likewi
se, compared to laterborn Sansei, firstborns seemed to be more informe
d and interested in Japanese values and culture and to have more cultu
rally traditional perspectives. Results support that, in general, comp
ared to laterboms, firstborns in both generations were more traditiona
lly ''Japanese''. Implications of these findings for understanding acc
ulturation are presented.