Iodine is a crucial micronutrient that is indispensable for optimal physical growth and cognitive maturation. However, the dietary iodine intake status of Macao’s population is unknown. Therefore, a cross-sectional study was conducted to assess the dietary iodine intake of Macao secondary school students. Four hundred and twenty-four students filled in a self-developed, 61-item, iodine-specific food frequency questionnaire (I-FFQ). The dietary iodine intake was calculated based on the I-FFQ and food composition database. The median daily iodine intake of the students was 74.4 µg, which is lower than the 150 µg recommended by the World Health Organization (WHO). The intake frequency of dried seaweed and kelp was also low, with 49.3% and 64.2% of students consuming these foods infrequently over a month. In conclusion, the dietary iodine intake of secondary school students in Macao was inadequate. It is recommended that individuals should take the initiative to gain iodine-related knowledge. Students are advised to eat a variety of iodine-rich foods, such as seaweed and seafood, as part of a healthy, balanced diet to ensure sufficient iodine intake. Furthermore, it will be necessary to measure urinary iodine for the iodine status assessment of the Macao population in future.