Abstract Background and purpose: Gestational diabetes mellitus (GDM) is the most common metabolic disorder in pregnancy. It was known one of the complications of this period. The aim of this study was to investigate the relationship between some risk factors with GDM in pregnant women in Zahedan, Iran. Materials and Methods: In a descriptive-analytical study, 70 pregnant women with GDM and 140 healthy pregnant women were selected referring to health and treatment centers in Zahedan by multistage sampling method. Weight and height were measured, and body mass index (BMI) was calculated using standard method. Other data were recorded by clinical examination, health record of anybody and interview in health centers. SPSS for Windows was used for statistical analysis. ttest and Chi-square test were used for comparison of two groups. P < 0.0500 was considered as a significant difference between groups. Results: As compared to controls the prevalence of GDM was more common in pregnant women who were older (P = 0.0001), high BMI (P = 0.0020), and more parity (P = 0. 0200), family history of diabetes (P = 0.0001) and macrosomia (P = 0.0100). There was significant difference between GDM with age (P = 0.0080), BMI (P = 0.0020), family history of diabetes (P = 0.0001), history of macrosomic infant’s birth (P = 0.0300). But it was not observed significant differences between GDM with smoking, history of hypertension, abortions, stillbirth, and preeclampsia. Conclusion: This study emphasizes to do GDM screening in the population of this area. It can be determined risk factors of GDM as moderate and severe status. Because GDM during pregnancy is associated with adverse outcomes.