Background: Birth weight is the most important indicator of infant's health, and this critical index is directly related to mother's health. Hence, knowledge of the maternal chronic disease before and during the pregnancy can be considered as an effective factor in maintaining the infant's ideal weight. Babies with low birth weight are more susceptible to risks such as disabilities of neurological, respiratory diseases and sudden infant death syndrome. Therefore, identifying and modifying the risk factors can control and prevent low birth weight. Objectives: This study was performed to determine the association between mothers' chronic diseases and low birth weight in infants. Methods: In this descriptive study, 1500 infants from 12 health centers in east and west areas of Ahvaz were selected using the random cluster sampling method. The developed researcher checklist was used for data gathering. The data was analyzed with SPSS version 20, using descriptive indexes and Chi-square, t-test and ANOVA while P ≤ 0.05 was considered as significant. Results:The prevalence of LBW in Ahvaz from the beginning to the end of the year 2015 has been 9.5%. There is a significant relationship between the cardiovascular disease before pregnancy (P ≤ 0.003), anemia before pregnancy (P ≤ 0.001), hypertensive pregnancy (P ≤ 0.001), urinary tract infection during pregnancy (P ≤ 0.001), gestational diabetic in the mother (P ≤ 0.003) and LBW. Conclusions: Our study showed that many mothers' schronic disease such as cardiovascular disease, anemia, hypertensive, gestational diabetic and UTI have relationship with LBW. Therefore it seems essential to design and implement a detailed antenatal care program for mothers with chronic disease to reduce LBW, infant mortality and defects.