Introduction: birth weight is one of the important sanitary indices in evaluating the prenatal care all over the world. The purpose of this research was to determine the relationship between the bio-environmental characteristics of mothers with infant’s birth weight. Materials and Methods: In corrolation study, first, all newborn babies in hospitals and maternity centers Khuzestan between Farwardin (May.2012) and Esfand (March.2013) were selected. Then, 925 babies were randomly selected and their parents answered the questionnaire of bio-environmental .The data analyzed with using correlation coefficient and multiple regression analysis. Results: there was a significant relation between the bio-environmental characteristics of mothers with infant’s birth weight (p<0/ 001). Also, results show that mother’s environmental features can explain 9% of the regression of the birth weight. Conclusion: recognition of some risk factors pertaining of low birth weight can help take preventive. The result showed that bio-environmental during pregnancy influences the birth weight.