Background: A significant shift in the health status of the Omani population was observed over the past five decades. The prevalence of Non-Communicable Diseases (NCDs) like cardiovascular diseases and diabetes became more prevalent compared to infectious diseases. Although NCDs caused by nutritional factors continue to increase rapidly Oman lacks dietary intake data that can be used to measure habitual dietary intake systematically. Food Frequency Questionnaires (FFQs) are one of the most commonly used dietary assessment methods in nutritional epidemiological studies. However, FFQs are population specific and need to be adapted to accurately represent the population being studied. Aim: Therefore, this research aims to develop and validate a reliable food frequency questionnaire specifically for the Omani adult population. Methods: This study employed both qualitative and quantitative methods. The Diet History Questionnaire II developed by the National Cancer Institute was used to guide the development of the newly developed Omani Food Frequency Questionnaire (OFFQ). Which was first modified to suite the Omani diet involving expert experiences of researchers and experts. In addition to cross-sectional market studies of food products in the local market. The OFFQ was then translated to Arabic language, back-translated to English, pilot tested with 13 volunteers. The OFFQ was then refined to be used in the reliability study. Usual dietary intake data was obtained from a semi-quantitative webbased questionnaire, inquiring about food intake over the past month. The questionnaire was administered twice with the second being filled after one to two weeks from the first questionnaire. The OFFQ was deployed in Arabic, and it consisted of questions inquiring about dietary intake, consumption frequency and portion, supplements intake and cooking methods. A convenience sample of healthy Omani adults (n= 62) was recruited from Sultan Qaboos University (SQU) employees and students. To assess the reliability of the OFFQ both internal consistency and test-retest reliability were assessed. Internal consistency was assessed by conducting Cronbach’s α test while test-retest reliability was assessed by comparing the median intake of food groups by calculating weighted kappa and intraclass correlation coefficients. Results: The OFFQ contained 136 food items and 8 dietary supplement questions which were divided into 15 food groups. Our study reported Weighted Kappa (kw) between the two OFFQ administrations showed fair to moderate agreement with kw values ranging from 0.38 to 0.60 for questions assessing the frequency of intake. While the median kw values between the two OFFQ administrations ranged from 0.26 to 0.58 for questions assessing portion size. The majority of food groups showed moderate to good test re-test reliability with median Intraclass Correlation Coefficients (ICCs) for food groups ranging from 0.516 to 0.807 for frequency questions and from 0.40 to 0.82 for portion questions. This trend of correlations shows moderate to good agreement for the majority of individual food items and food groups. On the other hand, the internal consistency showed good reliability (Cronbach’s α > 0.70) for only four food groups (1) Fruits, (2) Vegetables, potatoes, dried beans, (3) Meat, poultry, fish, (4) Sweets, baked goods, desserts. Conclusion: In conclusion, the newly developed OFFQ was deemed valid for the Omani dietary culture and is a reliable tool that can measure habitual dietary intake among Omani adults as evident by the reliability coefficients ranging from moderate to good agreement for the most food items and food groups.