Birth weight is an important factor in determining physical and mental growth of infant and is a valuable criterion to judge intrauterine growth. Therefore recognition of influencing factors on low birth weight and eliminating them are of great importance. This cross sectional study was conducted in 2001 to evaluate the relation between weight gain during first pregnancy and neonate’s birth weight. For this purpose 12 health houses were selected randomly in Kerman district and all files of primiparous women referring during the last 12 years (1989-2001) were chosen for collecting data (n=487). While educational level, profession, weight at the beginning of pregnancy, weight gain during the pregnancy and neonate’s sex had significant relation with neonate’s birth weight but, based on stepwise regression analysis weight at the beginning of pregnancy and mother’s education were significant as predictable factors of neonate’s birth weight. Concerning the increasing rate of maternal educational level, we hope to have less cases of low birth weight in near future. The results of this study show the importance of pre-pregnancy weight as an indicator to assess women at risk of delivering low weight neonates.