There are disclosed a process for producing an .alpha.-acyloxy-.alpha.,.beta.-unsaturated carbonyl compound represented by the general formula (VI): ##STR1## wherein R.sub.1, R.sub.2 and R.sub.4 are independently hydrogen atoms or substituted or unsubstituted hydrocarbon residues, or R.sub.1 and R.sub.2, when taken together with one another in an optional combination, form a ring, R.sub.3 is a substituted or unsubstituted hydrocarbon residue, and indicates that the configuration may be either E-configuration or Z-configuration, in particular, a 20-acyloxy-17(20)-methylen-21-al-steroid represented by the partial structural formula (II): ##STR2## wherein R is a hydrocarbon residue, and indicates that the configuration of the acyloxy group and the formyl group bonded to the carbon atom at the 20-position may be either E-configuration or Z-configuration, which comprises oxidizing a propargyl ester represented by the general formula (V): ##STR3## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 have the same meanings as defined above; an al-steroid compound having the above partial structural formula which is an intermediate for producing a 21-acyloxy-20-keto-delta.sup.16 -steroid being extremely useful as an intermediate for important corticoids as drugs and obtained by being subjected said al-steroid to isomerization reaction; and a process for producing a 21-acyloxy-20-keto-delta.sup.16 -steroid which comprises oxidation reaction and isomerization reaction.