The reaction rate was evaluated under continuous flow conditions using a standard tube reactor, a tube reactor with a static mixer and the honeycomb reactor (Scheme 2, Figure and Table ). The ratio of flow rates to internal volumes was unified in all the reactors. In the standard tube reactor, slug-flow was formed, and the conversion was 47% (entry 1). To evaluate the reaction rate for increasing the flow rate, the reaction solution was passed through the standard tube reactor three times (entry 2). The internal vortex was strengthened by increasing the flow rate, and the mixing efficiency was improved to give a higher reaction rate (67%). In the tube reactor with a static mixer, the reaction rate did not depend on the flow rate although the reaction conversion was higher than that in the standard tube reactor (entries 3 and 4). The tube reactor with a static mixer had a large inner diameter and the linear velocity became correspondingly low. The low linear velocity did not effectively affect the reaction rate. When the honeycomb reactor was set horizontally (entry 5), the reaction conversion was almost equivalent to that in the standard tube reactor. When the honeycomb reactor was set vertically (entry 6), the reaction rate greatly improved, and the reaction conversion was almost equivalent to that in the tube reactor with a static mixer. When the honeycomb reactor was set horizontally, oxygen gas was passed through the upper side of reactor and the reaction solution was passed through the lower side of the reactor. This heterogeneity resulted in low mixing efficiency and short pass of the reaction solution through the honeycomb reactor, which led to the low reaction rate. When the honeycomb reactor was set horizontally, the residence time distribution using the solution of 2a in the honeycomb reactor was much shorter than expected, which supported the above consideration (See Supporting Information File 1). The reaction rate was improved in a similar manner to entries 1 and 2 to give the highest reaction conversion (95%) when the reaction solution was passed through the honeycomb reactor three times (entry 7). When three honeycomb reactors were connected in series (entry 8), the reaction conversion was equivalent to that in entry 7, which showed that three cycles in a single honeycomb reactor and one cycle in three honeycomb reactors gave the same result. Entry 8 is a more suitable flow setup for manufacturing, but entry 7 is a more practical flow setup for laboratory experiments because the reaction conversion in each cycle can be analyzed. The porous structure in the honeycomb reactor improved the mixing efficiency like the static mixer, and the higher flow rate resulted in the higher reaction conversion. This evaluation showed the high potential of the honeycomb reactor for application to gas-liquid flow aerobic oxidation. Maximizing the throughput of aerobic oxidation using the honeycomb reactor