The deactivation of copper based catalysts for the hydrolysis of acrylonitrile to acrylamide has been studied using Raney copper and supported copper on silica catalysts. Initial rapid deactivation is due to the fouling of the surface by polymer produced from acrylamide. At least part of the polymer is formed by a process involving the catalysts. A second deactivation process caused by the interaction of the catalyst with oxygen is observed.This deactivation can be very significant with supported catalysts where small copper particles oxidise more easily. The activity of the catalyst after the initial deactivation is found to depend on the size of the pores in the catalyst.