α-Curcumene was isolated from the fresh aerial parts of Senecio selloi Spreng. DC. and its activity against bacteria, yeasts and an alga was inspected by the applying the microdilution method. The strongest effect was manifested against Saccharomyces cerevisiae with estimated values of MIC and MFC 0.8 mg/mL. The α-curcumene synergism in the concentrations of 1 mM and 5 mM, respectively, with selected antibiotics (ciprofloxacin, imipenem, ceftazidim and a combination of amoxicillin and clavulanic acid) was investigated against Staphylococcus aureus, Escherichia coli, Enterobacter cloacae, Staphylococcus haemolyticus and Klebsiella pneumoniae by the disk diffusion assay. The results have shown the occurrence of synergism of α-curcumene with imipenem against the clinical isolate E. cloacae with a significance level of p> 0.05. Based on these informations it can be concluded that fungal strains are more sensitive for α-curcumene than the bacterial ones and the synergism of α-curcumene with imipenem can improve the antibiotic efficiency against the E. cloacae.