The invention relates to a process for the preparation of acyl isocyanates of formula ##STR1## in which R is an alkyl radical, a substituted or unsubstituted naphthyl or phenyl radical or a substituted or unsubstituted aromatic heterocyclic radical, which consists in reacting an acyl halide of formula ##STR2## in which R has the above meaning and X denotes a fluorine, chlorine or bromine atom, with a sodium or potassium cyanate in the presence of a compound chosen from tin(IV), zinc or nickel(II) halides.The acyl isocyanates thus prepared are very useful for forming ureas or carbamates.