Diethylzinc (DEZ) is highly combustible in air and easily hydrolyzed in water, therefore research using this DEZ compound in the polymerization field has hardly been conducted. The present study shows the stabilization of DEZ by forming complex with 1,10-phenanthroline and succeeded in emulsion polymerization of styrene using this diethylzinc-1,10-phenanthroline complex (Phen-DEZ). Ultra-high-molecular-weight polymers (Mw > 1 x 10(7)) were obtained in high yield (80%) by using sodium dodecyl sulfate (SDS) as emulsifier in this emulsion system at 23 degrees C. The kinetics study of styrene emulsion polymerization initiated by Phen-DEZ was investigated. In the early stage of polymerization, an almost linear first-order kinetic plot was observed and the overall activation energy of this polymerization system was 31.0 kJ mol(-1).