Resumo. Allelopathy is characterized by harmful or benefic effects on the development of plants caused by chemical substances that are produced and released into the environment by a plant or microorganism. This study aimed to identify the possible allelopathic effects of Baccharis dracunculifolia DC. on mustard (Brassica campestris L.) and kale (Brassica pakinensis L.). It was realized tests in vitro (petri dishes) and decomposed leaves (ex vitro), being tested six leaves/aqueous extracts concentrations of B. dracunculifolia (10, 30, 50, 70, 90 and 100%) and then, compared to control (0.0%), soil or distilled water, with five repetitions each, being distributed ten seeds of the cultivated species in each repetition. Leaves of B. dracunculifolia showed allelopathic potentialon the germination of seeds, the germination speed index and on the initial growth of roots and fronds in the in vitro and ex vitrotreatments, being the decomposed leaves’ treatments more allelopathic for the both leafy vegetables tested, and these effects wereprobably due to the presence of secondary metabolites as flavonoids and tannins found in B. dracunculifolia. The results indicatean existence of allelopathic potential in B. dracunculifolia.