The effect of low pressure drop （LPD） mixer and Kenics mixer inserted in a tubular reactor on the mean resistence time distribution, pressure drop, and conversion for an irreversible, second-order reaction were investigated. From the results of the tracer experiment, it was found that the reactor could be simulated with n-Continuous Stirred Tank Reactors in series model. For empty tube, the deviations in conversion from a plug flow reactor (PFR) increase with the increase in the reactor diameter for the same mean resisdence time, whereas, with static mixers inserted in the tube the discrepancy of the conversion from a PFR was found to be 7 % regardless the magnitude of the reactor diameter. When a LPD mixer was inserted, the friction factor of the empty tube increased by a factor of 20 to 25.