Little is known about body mass index (BMI) patterns by nativity and length of US residence among Asian American ethnic groups. We used linear regression to examine the association of BMI with nativity and length of residence across six ethnic groups (Filipinos, Japanese, Chinese, Koreans, South Asians, and Vietnamese) using data from the California Health Interview Study. There was significant heterogeneity in the nativity/length of residence patterns in unadjusted BMI across ethnic groups (p < 0.001). In fully adjusted models, heterogeneity was attenuated (p = 0.05) with BMI among all US-born ethnic groups significantly higher than BMI for immigrants with the exception of South Asians. Longer US residence was positively associated with BMI among all groups, though only significant among Filipinos and Koreans. Programs targeting Asian Americans should take into consideration BMI patterns by nativity and US length of residence among diverse Asian American ethnic groups.