The allelopathic activity and chemical composition of the essential oil of Croton limae A. P. S. Gomes, M. F. Sales & P. E. Berry (marmeleiro-prateado) have been evaluated in this study. The essential oil was extracted by hydro-distillation. A completely randomized design was used to test the influence of the essential oil from fresh leaves of C. limae in concentrations of 0.10%, 0.25%, 0.50%, 0.75%, 1%, 1.25%, 2.50%, 3.75%, and 5% on the germination and growth of Lycopersicum esculentum Mill. (tomato) seeds by indirect contact, with a control using water and dimethyl sulfoxide (DMSO). Each treatment consisted of five replicates using twenty seeds in each one. The chemical analysis of the essential oil was carried out using gas chromatography coupled with mass spectrometry. The analysis showed the occurrence of 14 chemical compounds, the majority of which were cedrol (28.4%), eucalyptol (17.4%) and α-pinene (13.8). The C. limae essential oil inhibited germination of the tomato seeds at concentrations of 2.50% and upwards and it affected the caulicles and radicles of tomatoes at all concentrations tested. The tests proved that C. limae presents phytotoxic activities.