Introduction: Maternal obesity presents significant health risks to mothers and their fetuses. This study aimed to determine the proportion, associated factors and outcomes of maternal obesity among pregnant women in Klang Valley, Malaysia. Methods: A retrospective cross-sectional study was conducted between January 2018 and March 2018 using secondary data from the Malaysian National Obstetric Registry (NOR) for the year 2015. All pregnant women with first-trimester booking at 12 weeks and below that were registered with the NOR and met the inclusion and exclusion criteria were included in the study. Descriptive statistics and multiple logistic regression analysis were used. Data were analysed using SPSS version 22.0. A total of 2113 respondents were included in this study to determine the proportion, associated factors and outcomes of maternal obesity. Regarding the univariate and multivariate analyses, respondents were classified into two groups: normal and obese. The obese group comprised overweight and obese mothers. The underweight group was excluded in the subsequent analysis. Results: Out of the 2113 respondents, 7.1% were underweight, 41.7% were of normal weight, 28.6% were overweight, 15.9% were in obese class I, 4.6% were in obese class II, and 2.1% were in obese class III according to the WHO (1995) reference. However, when the MOH (2003) cutoff point was used, there was a marked increase in the proportion of respondents in the overweight categories by 2.7% and obesity class I by 12.8%. The Indian (AdjOR 2.06, 95% CI: 1.11, 3.83, p=0.021) and Malay (AdjOR 1.75, 95% CI: 1.02, 3.00, p=0.040) ethnicities, as well as both multiparity (AdjOR 1.46, 95% CI: 1.23, 1.73, p <0.001) and grand multiparity (AdjOR 2.41, 95% CI: 1.78, 3.26, p <0.001), were significantly associated with maternal obesity. There were significant association between maternal obesity with hypertensive disorder in pregnancy (p=0.025), caesarean section delivery (p=0.002) and macrosomic infant (p <0.001). Conclusion: The identification of risk factors for maternal obesity is important to facilitate intervention programmes focused on improving the pregnancy outcomes for a high-risk group of women.