Currently there is little research investigating awareness or use of dietary guidelines in Saudi Arabia. This study aims to investigate Saudi Arabian mother’s knowledge of current dietary guidelines regarding food groups and portion sizes and to investigate its relation to the sociodemographic factors. This cross-sectional study used community-based family events to recruit mothers and children. Health stands offering nutrition information and advice were used at these events for study recruitment and nutritional advices to attract them. A short online questionnaire was used to interview mothers during the events to measure their knowledge of dietary guideline and portion sizes. The questionnaire included questions to assess knowledge of dietary guidelines and portion sizes. Questions about the serving size of each food groups and the dietary guideline ‘MyPlate’ were included; the study recruited a convenience sample of 101 participants. Quantitative analysis using Chi-square and Kruksan-Wallis tests. We found 29.1 % of the participants were aware of the MyPlate guidelines and 51.5 % said that they are affected by healthy plate choices. Being married was significantly associated with knowing about the MyPlate Image (P= 0.004). Correct identification of food groups on the MyPlate Image and correct identification of serving sizes of food group was less than 50% for most food groups. A significantly greater percentage of those with a postgraduate education were accurate about the correct servings of fruit, vegetables and grains (P=0.049). Nutrition knowledge of food groups and serving sizes was poor in the sample of Saudi Arabian women. This research provides evidence that nutrition education is needed in the Saudi Arabia and the finding are relevant for future health promotion strategies. The study has also identified sociodemographic groups that possibly may need to be targeted with more attention in future nutrition education programs such as those with low income, lower education level and unmarried women.