Cyclotrimerization of acetylene was studied by means of atmospheric flow reaction at 373 K on Pd/titania catalyst to investigate variations of catalytic reactivity and product distribution. While ethylene and benzene were obtained as the major products, rapid decrease in acetylene conversion resulted from catalyst poisoning with the lapse of reaction time. For a fixed flow rate (space velocity 4,000 hr^-1), as acetylene concentrations decreased from 50 to 25, to 12.5 vol%, benzene yields decreased, whereas catalyst poisoning was attenuated. Comparison of benzene evolution signals from the variation of acetylene concentrations showed that the rate of benzene formation is first-order in acetylene pressure. In addition, for a fixed concentration (25 vol%) of acetylene, as space velocity increased from 4,000 to 6,000 hr^-1, benzene yields also increased and catalyst poisoning was attenuated. Optimization of acetylene concentration and flow rate may be necessary to accomplish the attenuation of catalyst poisoning as well as enhancement of benzene yield from acetylene cyclotrimerization by flow reaction. It can be deduced from this study that oxygen anion vacancies at palladium-titania interface and reduced titania made contributions toward catalytic activity for benzene formation at the temperature 100 K lower than those reported by previous researchers.