Background: Weight gain during pregnancy reflects the mother's nutritional status. However, it may be affected by nutritional therapy and exercise interventions used to control blood sugar in gestational diabetes mellitus (GDM). This study aimed to evaluate weight gain during gestation and pregnancy outcomes among women with GDM. Methods: A retrospective study involving 1523 women with GDM was conducted between July 2013 and July 2016. Demographic data, gestational weight gain (GWG), blood glucose, glycated-hemoglobin level, and maternal and fetal outcomes were extracted from medical records. Relationships between GWG and pregnancy outcomes were investigated using multivariate logistic regression. Results: In total, 451 (29.6%) women showed insufficient GWG and 484 (31.8%) showed excessive GWG. Excessive GWG was independently associated with macrosomia (adjusted odds ratio [aOR] 2.20, 95% confidence interval [CI] 1.50-3.52, P <0.001), large for gestational age (aOR 2.06, 95% CI 1.44-2.93, P < 0.001), small for gestational age (aOR 0.49, 95% CI 0.25-0.97, P. 0.040), neonatal hypoglycemia (aOR 3.80, 95% CI 1.20-12.00, P=0.023), preterm birth (aOR 0.45, 95% CI 0.21-0.96, P. 0.040), and cesarean delivery (aOR 1.45, 95% CI 1. I 3-1 .8 7, P= 0.004). Insufficient GWG increased the incidence of preterm birth (aOR 3.53, 95% Cl 1.96-6.37, P <0.001). Conclusions: Both excessive and insufficient weight gain require attention in women with GDM. Nutritional therapy and exercise interventions to control blood glucose should also be used to control reasonable weight gain during pregnancy to decrease adverse pregnancy outcomes.