AbstrakKebutuhan energi, protein, dan zat besi dapat disumbangkan oleh makanan jajanan masing-masing sekitar 36%, 29%, dan 52%. Namun, makanan jajan yang tersedia disamping tidak selalu sehat dan bergizi juga perilaku sisiwa tidak selalu positif untuk kebutuhan gizi. Tujuan penelitian ini mengetahui pengaruh media visual poster dan leaflet terhadap perilaku makanan jajanan pelajar suatu SMA di Kabupaten Mandailing Natal, Sumatera Utara, 2009. Dengan desain eksperimen kuasi one pre-and post-test group, penelitian dengan perlakuan pajangan poster dan leaflet di sekolah ini menilai pengaruh intervensi 2 minggu setelah perlakuan. Analisis data dilakukan dengan metode uji T-berpasangan terhadap sampel 80 pelajar kelas khusus. Sebelum dan setelah perlakuan, skor rata-rata pengetahuan siswa adalah 1,99 dan 3,00, skor rata-rata sikap adalah 1,80 dan 3,00. Tindakan konsumsi makanan para pelajar juga meningkat sebelum (x=1,76) dan sesudah (x=1,86) intervensi. Terdapat perbedaan yang bermakna antara perilaku konsumsi makanan jajanan pada anak sekolah sebelum dan sesudah intervensi. Dapat disimpulkan bahwa penyuluhan gizi menggunakan media poster dan leaflet mampu meningkatkan perilaku gizi anak sekolah. Disarankan pihak sekolah dan puskesmas menggunakan poster dan leaflet sebagai salah satu media penyuluhan gizi menyampaikan informasi gizi tentang makanan jajanan dan isu kesehatan lain untuk mempromosikan upaya kesehatan sekolah.Kata kunci: Perilaku konsumsi makanan jajanan, poster dan leaflet, pelajar SMA Abstract Street food plays an important role in students' nutrition. About 36%, 29%, and 52% of energy, protein, and iron, respectively, can be contributed by street food. The aim of the research was to know effect of nutritional extension using healthy food poster and leaflet on street food consumption behaviour among Senior Height School students in District of Mandailing Natal. The research is quasi-experiment with one pre-and post-test group design. The intervention was conducted by displaying poster and giving leaflet to students. Effects of interventions were evaluated two weeks after intervention. Subjects are 80 students. Data were analyzing by using paired sample T-test. Result showed that the average scores of knowledge of students were 1.99 and 3.00 before and after intervention, respectively. The average scores of attitude were 1.80 and 3.00 before and after intervention, respectively). Also, the practice of food consumption among students also increases (1.76 and 1.86 for before and after intervention, respectively). There was a significant difference in street food consumption behavior among students between before and after intervention. It can be concluded that nutritional extension using visual posters and leaflets increase student's nutritional behaviour. It is suggested that, both school and puskesmas, use poster and leaflet as media of nutritional extension regarding street food and other health issues to promote school health Keywords: Street food consumption behaviour, poster and leaflet, senior hig...