The robust data about myo-inositol (Myo-Ins) safety profile and effectiveness opened a new scenario for the treatment and prevention of Gestational Diabetes Mellitus (GDM). We report our experience about a case of GDM successfully treated with Myo-Ins. An overweight 29-year-old Caucasian pregnant woman, nulliparous, affected by GDM, according to the National Institute for Health and Care Excellence (NICE) Guideline. After diagnosis, the patient underwent regular glycemia checks: mean fasting blood glucose value was 103.63 ± 1.46 mg/dl, whereas 1-hour and 2-hours after-meal values were 122.74 ± 11.14 mg/dl and 110.74 ± 10.70 mg/dl, respectively. We decided to prescribe a low-calorie diet and oral treatment with 4 g of Myo-Ins, 3 times per day for 3 weeks. After the treatment, mean fasting value was 90.74 ± 5.30 mg/dl, whereas 1-hour after and 2-hours after-meal values were 108.11 ± 6.05 mg/dl and 101.21 ± 4.78 mg/dl, respectively. We reported a significant decrease of glycemia in a faster and steady way at fasting, 1-hour and 2-hours after-meal post oral treatment with 4 g of Myo-Ins 3 times per day, in a patient affected by GDM. On the one hand, we could confirm the safety profile of the molecule also at this high dosage, free from any side effects; on the other hand, our experience highlighted the faster glucose-lowering effect due to a higher dose of Myo-Ins. This outcome may open a new scenario in the treatment of GDM.