An approach for analysis of thermal gradients in a catalytic packed bed milli-reactor operated under radio frequency (RF) heating has been presented. A single-point temperature measurement would cause the misinterpretation of the catalytic activity in an RF-heated reactor, because of the presence of a temperature gradient. For reliable data interpretation, the temperature should be measured at three positions along the reactor length. The temperature profile can be accurately estimated with the exact analytical solution of a one-dimensional (1D) convection and conduction heat-transfer model, and it can also be approximated with a second-order polynomial function. The results revealed that the position of maximum temperature in the catalytic bed shifts toward a downstream location as the flow rate increases. The relative contribution of conduction and convection to the overall heat transport has been discussed. The design criteria for a near-isothermal milli-reactor have been suggested.