Disclosed is a catalyst for the oxidative dimerization of toluene, comprising a composition represented by the general formula:Tl.sub.1 M.sub.a M'.sub.b O.sub.cwhereinM represents at least one element selected from the group consisting of beryllium, magnesium, calcium, strontium and barium; M' represents at least one element selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, titanium, zirconium, hafnium, niobium, tantalum, zinc, aluminum, gallium, indium and antimony;a is 0.05 to 15;b is 0.05 to 15;c is a number determined by the valences of thallium, M and M';with the proviso that the number of alkali metal atoms is at most 20% of the number of total atoms constituting the catalyst except for oxygen when alkali metal is included in M', and a process for producing 1,2-diphenylethane and 1,2-diphenylethylene by the oxidative dimerization of toluene in the presence of a catalyst comprising a composition represented by the above-mentioned general formula.