The current study elucidates the responses of a typical ornamental plant Mirabilis jalapa to exhausted engine oil (EEO) during phytoremediation. Greenhouse experiments were established to assess the plant’s response in terms of germination, biomass, chlorophyll content, superoxide dismutase (SOD) activity, catalase activity, soluble protein content, and hydrocarbon degradation at different concentrations of EEO (0.5 to 15 mL). Results illustrate that the increasing concentration of EEO reduced plant growth, whose responses were further confirmed by decreased chlorophyll content (chlorophyll a and b), high superoxide dismutase activity, lowered catalase activity, and reduced soluble protein content. Although the germination rate was successful in all the treatments, we observed a significant reduction in biomass – especially the elongation inhibition rate (>48.4%) – at EEO concentrations higher than 2%. Conclusively, the high toxicity index (40.4% to 93.3%) and lesser hydrocarbons degradation (36% to 10.8%) render the plant species unsuitable for future EEO phytoremediation experiments.