This article describes a laboratory micro downer (MD) unit, that can be used for fluid cracking (FCC) unit as well as for steam catalytic cracking or selective oxidation. Its performance is compared with that of a fixed bed micro activity test (MAT) and a Davison circulating riser (DCR) riser pilot plant using a commercial FCC catalyst and a standard vacuum gas oil. MD unit simulates a steady state operation similar to FCC riser, catalyst and feedstock being continuously fed and removed during test. This new unit allows a large operation flexibility, being able to work at very low contact times (300 ms) in a wide range of reaction temperatures and catalyst to oil ratios. Important differences are found in product distribution comparing MAT and MD at same reaction temperature and range of conversion. Differences can be explained considering the lower catalyst residence time in the MD unit, leading to lower yields of H-2 and dry gas, higher olefinicity in the LPG fraction, and lower amount of coke on the catalyst. In contrast, MD data fit better the yields obtained with DCR pilot plant, especially yields of high interest as isobutene and coke.