Photochromic solid-state trans-cis isomerization of the 4-aminoazobenzene moiety was observed for the first time in (trans-4-aminoazobenzene)(beta-cyanoethyl)bis(dimethylglyoximato)cobalt(III) after beta-alpha isomerization of the beta-cyanoethyl group on exposure to UV light. The UV spectra revealed that beta-alpha isomerization occurred first, followed by the trans-cis transformation. When the crystal was exposed to visible light, only the beta-alpha isomerization of the cyanoethyl group occurred, with retention of the single-crystal form. The crystal structure before and after the beta-alpha photoisomerization showed that the isomerization is important in this photochromic trans-cis transformation.