RESUMO -Os objetivos deste estudo foram avaliar Azolla caroliniana como planta-teste em estudos ecotoxicológicos e estimar a CL50;7d dos herbicidas 2,4-D, glyphosate, clomazone e oxyfluorfen. As plantas foram aclimatadas em sala de bioensaio. Para isso, foram selecionadas cinco plantas em 50 mL de meio de cultivo Hoagland. Palavras-chave: bioindicador, toxicidade aguda, produtos fitossanitários, macrófita.ABSTRACT -The objectives of this study were to evaluate Azolla caroliniana as test plant in ecotoxicological studies and to estimate the LC50; 7d of the herbicides 2,4 D , glyphosate, and clomazone oxyfluorfen. The plants were acclimatized in the bioassay room. Five plants in 50 mL Hoagland culture medium were selected. After that, 50 mL of Hoagland and the herbicide were added, completing the volume to 100 mL. The 50% lethal concentration (LC50; 7d) for A. caroliniana exposed to the herbicide 2,4-D, was 708.35 mg L -1 ; to glyphosate (formulation Scout ® ), 23.66 mg L -1 ; to glyphosate (formulation Trop ® ), 38.91 mg L -1 ; to clomazone, 129.63 mg L -1 ; and to oxyflourfen, 80.50 mg L -1 . The herbicides glyphosate (Scout ® and Trop ® ) and oxyflourfen were classified as moderately toxic to A. caroliniana, while clomazone and 2,4-D were classified as practically nontoxic. It was concluded that A. caroliniana plants can be used as bio-indicators for glyphosate and oxyfluorfen-based herbicides.