Introduction: Various factors affect the health of both mother and fetus which maternal nutrition is one of them. Weight gain in pregnancy is one of the valid criteria for assessing nutritional status. The aim of this study was to investigate the relationship between weight gain in pregnancy and birth weight in Yazd city. Methods: This was a cross-sectional study. Data of 200 pregnant women 16 to 40 years that referred to health centers of Yazd were studied.low birth weight and normal weight in infants were considered less than 2500 gr and more than 2500 gr, respectively. Data were analyzed through SPSS 16 software. Results: The Mean age of the study was 26.65 years. Weight gain during pregnancy was 12/39 kg. The mean birth weight was 3147 gr of which 7.5 percent (n = 15) LBW and 92/5 percent (185 patients) had normal weight. Mean of BMI was 24.08 kg/m2 in study group. The correlation between maternal weight gain during pregnancy and birth weight was not significant. Conclusion: birth weight may be affected by other factors such as general and mental health of the mother and number of pregnancies, so by identifying these factors more careness than of pregnant women can be taken.