To provide a method for producing a vinylideneolefin in higher yield and in an extremely shorter time than in a well-known method.

A vinylolefin is dimerized by using at least one trialkylaluminum compound as only one catalytic component to be packed into a reactor. These substances are added to the reactor so as to contain 0.001 to 0.05mol of the trialkylaluminum based on the initial vinylolefin. The reaction is carried out at a temperature higher than 140°C and lower than 172°C for a sufficient time of 1-24 hours to convert at least 10wt.% of the initial vinylolefin in at least 80wt.% vinylidene dimer selection ratio.