A process for synthesizing aryltretinoin and aryltretinoin ethylester, used for preparing capsules to treat psoriasis, includes such steps as reaction between [1-(5,6,7,,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)-ethyl]-phosphine triphenylbromide and p-ethoxycarbonyl benzaldehyde in isopropanol to obtain P-[(E)-2 -(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl) propenyl]-ethyl benzoate, that is, aryltretinoin ethylester, and adding it to alcohol to synthesize P-[(E)-2 -(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl) propenyl]-benzoate, that is, aryltretinoin.