The rates of overweight and obesity are rising to epidemic proportions globally, especially among women. Obesity is increasingly common in the obstetric population as well. Sri Lanka is not an exception to this regard. There is limited published data on maternal perceptions on obesity in pregnancy, gestational weight gain and its complications. The current study aimed to describe the maternal perception on obesity, their knowledge on complications of obesity in pregnancy and gestational weight gain in pregnant mothers. Hospital based descriptive cross sectional study was conducted among a systematic sample of 416 pregnant women registered for antenatal clinic care at De Soyza Maternity Hospital. Pre-tested interviewer administered questionnaire was used for data collection. Maternal BMI at booking visit was taken from the pregnancy record to assess the overweight/obesity prevalence among the study population. Nearly one third (32.2%) of the study population were overweight and 11.8% were obese. Fifty three percent (53%) of overweight women identified themselves as such, but 45% of them considered themselves to be normal weight. Most of the pregnant women in the study sample (59.6%) were unable to estimate the recommended weight gain in pregnancy. Women's knowledge on the specific risks associated with maternal obesity was poor. Pregnant mother's knowledge on obesity, gestational weight gain and its consequences were unsatisfactory. Bridging this knowledge gap is an important step towards improving perinatal outcomes for all pregnant mothers in the current obesity epidemic.