The purposive of this descriptive correlational study was to examine the relationship i between personal-factors, health promoting behaviors during pregnancy and newborn's birth weight delivered. The subjects composed of 300 postpartum mothers selected by purposive i sampling. The inclusion criterion was postpartum mothers who admitted at postpartum ward 2 at Udonthani hospital. The data were collected by using three questionnaires consisted of I personal data form, antenatal and newborn's birth weight record and Health promoting behaviors I during pregnancy questionnaire modified from Nonprasert et al. (2008). The Health promoting I behaviors during pregnancy questionnaire was evaluated for content validity by five experts. I The Cronbach's Alpha Coefficient was 0,77. Data were analyzed by using percentage, mean, standard deviation, Crosstabs, Pearson product moment correlation, Spearman rank-order correlation coefficient, Chi-Square Test and Contingency coefficient. The major findings were as follows : 1. The.overal1 health promotimg behavior during pregnancy and each component were I rather good. 2. Four personal factor are Age, Gastational age, Weight gain during pregnancy, and Complication during pregnancy were correlated to birth weight infants at a significance level of 0.05. 3. There was no correlation between the overall components of health promoting behaviors during pregnancy and newborn's birth weight. Only one component of this questionnaire, interpersonal Relations was positively and significantly related to newborn's birth weight (r=0.15, p