Objective: To determine the frequency of hypovitaminosis B12 in pregnant females presented with gestational diabetes mellitus. Study Design: Retrospective study Place and Duration: The department of Gynaecology and Obstetrics, Category A Hospital, Batkhela Malakand and Muhammad Teaching Hospital, Peshawarfor the duration of six months from October 2020 to March 2021. Methodology: Total 190 pregnant women (95 GDM, 95 non-GDM) were enrolled in this study. Patient’s ages were ranging between 18 to 40 years. Detailed demographics including age, gestational age, body mass index (BMI), and gravidty were recorded after taking informed written consent. Blood samples were taken from all the patients for measuring vitamin B12 status. Hypovitaminosis B12 was defined as <300 pg/ml. Data was analyzed by SPSS 24.0. Results: Mean age of patients was 32.46±6.82 years. Mean BMI was 26.24±2.34 kg/m2. Mean gestational age was 34.56±2.18 weeks. 105 (55.26%) women were multigravida. 80 (42.11%) patients had vitamin B12 level <300 pg/ml. Patients with GDM had high rate of vitaminosis B12 deficiency as compared to non-GDM patients (65.26% Vs 18.95%). A significant association was observed between GDM and hypovitaminosis B12 with p-value <0.0001. Conclusion: Vitamin B12 deficiency was significantly associated with gestational diabetes mellitus with frequency of 65.26%. Keywords: Vitaminosis B12, Gestational Diabetes Mellitus, Pregnancy