Ambrosia is the most common weed species of root crops in continental Croatia. It is an extremely aggressive weed species and due to its characteristics it is considered invasive. It causes significant losses in crop yields and is a major public health problem due to pollen, which is a strong allergen for humans and animals. The purpose of this research was to confirm, by the bio-test method, susceptibility of ragweed to the herbicides foramsulfuron, prosulfuron, thifensulfuron and imazamox. Plants were grown in the greenhouse and in the development phase BBCH 12-14 were treated with linearly decreasing dosing of investigated herbicides (2x - 1 / 64x; x = registered dose of herbicides). The sensitivity of ragweed was determined by visual assessment of damage, 7, 14, 21 and 28 days after treatment (DAT) and reduction of dry above ground mass (28 DAT). The results of the study show that all four investigated herbicides are effective on ragweed, but also that ragweed is differently sensitive to the researched herbicides. Symptoms progressively increased from the first assessment (7 days after treatment-DAT) from the last (28 DAT) for all herbicides investigated. The strongest phytotoxic symptoms was found with in the herbicide foramsulfuron (94% - 28 DNT), and the smallest with imazamox (78% - 28 DNT) at registered herbicide dosages. Dose-response curves were used to estimate dosing for reduction 90% of fresh above ground ragweed mass (ED90): foramsulfuron = 10.11 g ha-1, thifensulfuron = 5,34 g ha-1, imazamox = 102.4 g ha-1. The obtained data indicate that ragweed showed different sensitivity depending of the active substance of the ALS herbicide, so the herbicides were ranked according to the estimated dose required to reduce 50 or 90% of the above ground ragweed mass (from better to worse): prosulfuron<foramsulfuron<tifensulfuron<imazamox.