Bis(ethylxanthato)nickel(II) was identified by FTIR, DSC, MS and X-ray powder diffraction methods. It has a monoclinic structure with cell parameters of a=14.800(3)A, b=14.088(1)A, c=13.274(8)A; beta=101.13 degrees(8)degrees. It decomposes at above 170 degrees C. Styrene oxide was polymerized with bis(ethylxanthato)nickel(II) under air, nitrogen and vacuum conditions. The structure of the resulting polymers was determined by means of FTIR, C-13 NMR, X-ray diffraction, vapor pressure osmometer and DSC. Low molecular weight and partially crystalline polymers have regular head to tail and irregular head to head structure indicating that the oxirane ring opened both at alpha (-CH-O) and beta (-CH2-O) positions. Ring opening reaction proceeds via cationic or/and coordination cationic mechanism with formation of oxonium ion.