The most typical metabolic disease that can affect pregnant women, gestational diabetes mellitus is linked to substantial maternal and newborn consequences. Typically, this anomaly is discovered in the late stages of pregnancy. This study aims to assess the knowledge and attitude regarding management of gestational diabetes mellitus among antenatal mothers attending OPD in tertiary care hospitals of Sikkim. A descriptive cross-sectional study was conducted, comprising a total of 162 antenatal mothers who visited the OPD at the CRH and STNM hospitals. The antenatal mothers were assessed between 19 to 38 weeks of gestation. Structured knowledge questionnaire and 5-point Likert Scale was used to assess the knowledge and attitude regarding management of gestational diabetes mellitus of antenatal mothers. Data entry and statistical analysis was performed with the help of SPSS version 20. The study found that, out of 162 mothers, 111 (68.5%) had average knowledge, 34 (21%) had poor knowledge, and 17 (10.5%) had good knowledge about the management of gestational diabetes mellitus. In addition, 147 (91%) of antenatal mothers expressed positive attitudes towards managing gestational diabetes mellitus, while 15 (9%) had negative attitudes. The study concluded that the majority 68.5% of antenatal mothers had average knowledge, but 10.5% had a good knowledge of gestational diabetes mellitus (GDM). Since this kind of research is very helpful in preventing consequences, more studies should be conducted as well as promotion initiatives through health education before and during pregnancy to raise awareness of GDM and its management.