Aim: This study aimed to assess the awareness about gestational diabetes mellitus (GDM) among married females in Jeddah, Saudi Arabia. Methods: A cross-sectional study was done on all women in reproductive age and an electronic questionnaire was used. Data about participants’ demographics, parity, BMI, pregnancy, family and personal history of chronic diseases, gestational diabetes were collected. Their knowledge about effect of gestational diabetes on mother and on neonatal outcomes and their source of information about GDM were assessed. Results: The mean age of the participants was 37.99 ± 9.44 years and 77.8% of them had poor knowledge about GDM and 6.1% had good knowledge. Multipara women with a university education had a significantly higher mean knowledge level and the most common source of participants’ knowledge about GDM was social media. Conclusion: Females’ knowledge about GDM was significantly low in Jeddah. Health education campaigns and mass media education are urgent to increase their awareness about GDM. Health care practitioners should focus on popularizing GDM and raising awareness of its consequences.