The structure and reactivity of dialkylmagnesium–2-alkoxyethanol system as an initiator for styrene polymerization were studied. Dialkylmagnesium coupled with an equimolar quantity of 2-alkoxyethanol was found to initiate styrene polymerization, although the use of dialkylmagnesium alone could not induce polymerization. Metalation reaction of fluorene and addition reaction to 1, 1-diphenylethylene were possible with dialkylmagnesium–2-alkoxyethanol system. Measurements of the electronic spectra of these carbanion solutions indicated that coordination-agentseparated ion pairs were produced in the system. The colorless prism crystal, which was formed in di-n-butylmagnesium–2-methoxyethanol system, was found to possess a composition such as n-C4H9MgOCH2OCH3·OCH3·Mg(OCH2CH2OCH3)2. This complex exhibited high reactivity for styrene polymerization.