Abstract: This study was designed to determine the relationship between Maternal Iron Supplement (MIS) and Birth Weight (BW) in a rural area in North of Iran. A sample size of 2881 children was chosen by cluster and random sampling from 20 villages. MIS status, BW and demographic characteristics were recorded. Data was analyzed by SPSS 15 software and statistical significance was defined as p<0.05. Mean and SD of BW is 3177.2±522.6 g. Taking iron supplement by mothers with low birth weight, normal birth weight and high birth weight were shown 96.1, 94.9 and 87.1%, respectively. MIS increased birth weight only in younger mother, <5 family number and <3rd birth order but there is no statistical significant. Logistic regression showed that younger mother (p = 0.014, OR = 2.181), Low income (p = 0.001, OR = 1.601) and primary birth order (p = 0.001, OR = 1.738) are risk factor for low birth weight. MIS only in younger mother, low economic status and primary birth order led to improve birth weight. Maternal age, economic status, birth order and ethnicity are risk factors for low birth weight.