Surveillance result from premises in four districts of Hanoi on using oil/fat and determine peroxide value, Kreiss reaction and Benzo(a)pyrene content in reused oil/fat in some premises of fried cakes, green onion in Hanoi in 2012 showed that: - Proportion of premises reusing oil/fat (84 percent), proportion of premises reusing oil/fat daily (96.4 percent). - Proportion of premises conforming to food safety regulations (27 percent), proportion of premises having contracts with food provider (for oil/fat) which conforming to food safety regulation (35 percent), proportion of premises having invoice of oi//fat daily purchase (56 percent). - Persons who do frying directly at premises of fried cakes, and onion are mainly female (83.3 percent). Education level of these persons is mainly high school. - Proportion of persons who do frying directly at premises of fried cakes, and onion having good practices on reusing oil/fat was 53.9 percent, proportion of having workware outfit (46.1 percent), proportion of these persons wearing bracelets, rings during processing was 36.3 percent, proportion of reusing oi//fat for more than 3 times was 46. 1 percent. - Proportion of persons who do frying directly at premises of fried cakes and onion having knowledge on times of reusing oi//fat (68.7 percent), in which proportion of persons knowing that many times of reusing oi//fat hanns human health was relatively high (88.7 percent). - Proportion of reused oil/fat samples having positive result of peroxide was 16 percent. Proportion of samples having positive Kreiss reaction (+) was 100 percent, in which Kreiss (++) was 24 percent, Kreiss (+++) was 76 percent.