(1)Objectives: The effect of Symbiotic supplements on some biochemical characteristics in women with gestational diabetes mellitus. (2 )Design: Randomized Double blind clinical Trial. (3)Setting and conduct: The process of Balanced Block selection were performed until all the 90 patients were random divided into 2 groups. The first blood samples were taken from the subjects after assessing their anthropometric measurements and taking their 24 hour food recalls. Then, they were asked to consume either of the symbiotic or placebo capsules for 6 weeks. Subjects were asked not to consume any symbiotic-containing food, yogurt or its products during the intervention. More so, they were asked not to change their regular diet, activity and medicine during the study. Second Blood samples were also taken after an overnight fasting and before-after analysis was performed finally. (4)Participants including major eligibility criteria: (4-a) Major Inclusion Criteria: Women with gestational diabetes mellitus. (4-b) Major Exclusion Criteria: A history of diabetes before pregnancy; blood pressure; tobacco and alcohol use; Having Eclampsia and pre-eclampsia; clinical signs of some chronic or acute diseases. (5)Intervention: Group 1 (Intervention group) who daily received 1 capsule containing 500 mg probiotic supplements after the lunch meal, and Group 2 (Placebo group) who received placebo as the same, all for 6 weeks. (6)Main outcome measures (Variables): Fasting blood sugar, Serum insulin, Total Cholesterol, LDL-C, HDL-C, TG and HOMA-IR, Insulin sensitivity