Birth weight (BW) is an important determinant of infant's well being. Several factors such as mothers' genetic characteristics, socio-cultural, demographic, behavioral factors, prepregnancy body mass index (BMI), gestational weight gain (GWG) etc contribute to birth weight. This study assesses the anthropometric measurement of ethnic Nepalese women belonging to Sherpa/Tamang community and Brahmin/Chhetri community and the neonatal outcome in this population. A retrospective study was done in singleton pregnant women of Sherpa/Tamang and Brahmin/Chhetri community who delivered baby in Nepal Medical College and Teaching Hospital from April 2007 to March 2008 to examine the association between the maternal Body Mass Index (BMI) and the gestational weight gain among the two ethnic communities and the birth weight of newborns. Among 206 Sherpa women who met the eligibility criteria, the mean BMI of Sherpa/Tamang community was 23.53 +/- 2.28 which was statistically higher than the Brahmin/Chhetri community (21.6 +/- 2.32). Among Sherpa/Tamang community, the mean gestational weight gain was 12.8 +/- 3.4 kg and the mean birth weight was 3460 +/- 410 grams. Similarly among Brahmin/Chhetri community, mean gestation weight gain was 10.3 +/- 3.1 kg and the mean birth weight was 2960 +/- 340 gm. Maternal BMI, gestational weight gain and birth weight of the newborn was significantly higher in Sherpa/Tamang community and the Increasing BMI and the gestational weight gain was found to have strong association with the birth weight of the newborns among this ethnic community.