In the present study, six monoterpenes and twophenylpropenes were evaluated for their antibacterial effect against three phytopathogenic bacteria, Agrobacterium tumefaciens, Ralstonia solanacearum and Erwinia carotovora var. carotovora. The inhibitory effects of these compounds on polygalacturonase and dehydrogenases activities were also tested. The results revealed that trans-cinnamaldehyde, (-)-citronellal, (-)-terpinen-4-ol had the highest antibacterial activity against A. tumefaciens. Their minimum inhibitory concentration (MIC) values were 1000, 1500 and 1500 mg/l, respectively. Similarly, trans- cinnamaldehyde (MIC = 2000 mg/l), and (-)-citronellal (MIC = 2000 mg/l) were the highest activity compounds against E. carotovora var. carotovora. Moreover, (-)-citronellal caused the greatest antibacterial effect against R. solanacearum with MIC value of 1000 mg/l. Further, trans- cinnamaldehyde showed the highest inhibitory effects on polyglacturonase and dehydrogenases activities of A. tumefaciens, while (-)-citronellal represented the most potent effect of inhibition on polyglacturonase and dehydrogenases activities of E. carotovora var. carotovora and R. solanacearum.