Backround: GDM is defined as “glucose intolerance that is detected during pregnancy” (1) or “carbohydrate intolerance resulting in hyperglycaemia of variable severity with onset or first acknowledgment in the course of pregnancy. Aim: The main aim of the study to assess the knowledge and attitude on gestational diabetes mellitus (GDM) among obese pregnant mother. Methods: Cross sectional study design was used for the study. The study was conducted in a selected hospital at Chennai. Using the convenient sample technique method the 175 obese pregnant mothers were selected for the study. Finding: The study revealed that majority (70.86%) recognize a positive family history as a GDM risk factor, with nearly all (98.29%) aware of obesity-related discomforts during pregnancy, including dyspnea on exertion (81.14%), hypertension (80.57%), and diabetes (73.71%). Attitudes toward gestational diabetes mellitus (GDM) are highly proactive, with 90.6% viewing it as a serious condition and 91.6% believing its complications are preventable. There is unanimous support (100%) for routine screening and regular blood glucose testing, but only 71% are willing to exercise regularly due to fatigue (94.4%). Conclusion: The study concluded that the study indicates that the knowledge level about gestational diabetes mellitus (GDM) among obese antenatal mother having moderate knowledge. Despite this, obese antenatal mothers exhibit positive attitudes towards managing and preventing GDM.