Measurements of catalyst temperature and outlet conversion on a metal honeycomb system give evidence that the CO oxidation may proceed chaotically in time over a range of inlet CO concentrations and temperatures. The catalyst used in this study was represented by a very thin layer of α-Al 2O 3, deposited on a metal honeycomb matrix, impregnated by Pd. Measurements were performed for 0.5, 1, 3, 5 and 7% CO. Theoretical calculations and experimental evidence indicated that pore and gas-to-solid heat and mass transfer are absent. For higher inlet temperatures chaotic oscillations become more “symmetrical” and finally disappears. For 1% CO the effect of surface memory was observed.