The widespread use of agrochemicals for controlling pests and diseases of crops is recognized as a main threat tobiodiversity. Sulfonylurea herbicides are being increasingly used and display low levels of degradation in waterwhich suggest that they might affect non-target organisms. In a common garden experiment, eggs of a widespreadamphibian (Bufo spinosus) were exposed to sublethal environmentally relevant concentrations of a widelyused sulfonylurea herbicide, nicosulfuron, during the whole embryonic development. We assessed developmentrelatedtraits (i.e., development duration, hatching success, hatchling size and occurrence of malformation) aswell as antioxidant markers in response to contamination (i.e., SOD, GPx, catalase, thiols and relevant ratiosthereof). We found that sublethal concentrations of nicosulfuron increased embryonic development duration,increased hatchling size and tended to increase malformations. Embryos exposed to nicosulfuron displayeddecreased thiols and increased catalase activity suggesting alteration of oxidative status. We did not find anyeffect of nicosulfuron on SOD and GPx levels. Interestingly, higher catalase activity was linked to higher proportionof malformed individuals, suggesting that exposure to nicosulfuron induced teratogenic effects. Ourresults suggest that alteration of antioxidant levels might be one physiological mechanism through which nicosulfuronmight cause detrimental effects on amphibian embryos. Sublethal effects of pesticides at environmentallyrelevant concentrations have been overlooked and require further investigations, especially in nontargettaxa occurring in agricultural landscapes.