Abstract: A method of preparing 1-butene and/or hexenes resides in dimerization of ethylene and/or co-dimerization of ethylene and propylene in an organic solvent under an increased pressure and at a temperature of 0.degree. to 100.degree. C. in the presence of a complex organometallic catalyst. The catalyst contains titanium alcoholate of the formula Ti(OR.sup.1).sub.4, where R.sup.1 is an alkyl radical having from 1 to 8 carbon atoms or aryl, trialkylaluminium of the formula AlR.sup.2.sub.3, where R.sup.2 is an alkyl radical having from 1 to 6 carbon atoms, an organomagnesium compound of the formula MgR.sup.2.sub.2 and/or MgR.sup.3 X, where R.sup.3 is an alkyl radical having from 1 to 4 carbon atoms and X is Br, Cl, or I.