Over the temperature range 377° to 448 °C, vinyl ethyl ether has been found to decompose by a first order reaction to give ethylene and acetaldehyde, at a rate given by[Formula: see text]The reaction is capable of sensitizing the decomposition of acetaldehyde and the polymerization of ethylene; this indicates that free radicals are produced during the decomposition of the ether.Nitric oxide exerts virtually no effect upon the rate of ether decomposition, although it does reduce the rates of pressure change of ether-acetaldehyde mixtures to those corresponding to ether decomposition alone.It is suggested that the decomposition of vinyl ethyl ether occurs essentially through a rearrangement mechanism, and that free radicals do not play an important part, owing possibly to the inhibiting character of this unsaturated ether.