The effects of complexed metal ions on trans-cis photoisomerization reactions of two azobenzene compounds having a crown ether ring, 1a (small ring) and 1b (large ring) were investigated. The photoisomerization of 2,2’-dimethoxyazobenzene (2) was compared as a control. Anomalous increase in the quantum yields of the photoisomerization of 1a and 1b were observed by complexation with alkaline earth metal ions in both cases of photo irradiation at n-->pi* and pi-->pi* absorption bands, except for some cases. These increase was attributed to the interaction between coordinated metal ions and oxygen atoms on 2,2’-position and/or nitrogen atoms of the azobenzene moiety. The dependence of the quantum yields on the ring size of the crown ether was also discussed.