Abstract: A method is disclosed for controlling the polymerization process of olefinic hydrocarbons in an inert solvent which provides continuous control of Mooney viscosity and molecular weight distribution of the obtained polymer. In the disclosed method, means (4, 5) are included for measuring the temperature of a polymer solution in different parts of a reactor (1) provided with agitation (2), as well as means (6) for measuring the dynamic or kinematic viscosity of the polymer solution and means (7) for measuring the polymer concentration in the solution. A valve (8) mounted on the catalyst feed line controls the catalyst flow rate. A computer (9) is used to control the entire process by calculating the Mooney viscosity from the dynamic viscosity and polymer concentration and adjusting the process parameters as necessary to achieve a pre-set Mooney viscosity.