Quantitative measurements on long-chain branching in polyethylene have not been established. This paper presents a method available for calculating the degree of long-chain branching and the exponent α in the hydrodynamic relation g = Gα(where g is the ratio of the intrinsic viscosities of branched and linear molecules at the same molecular weight, and G is the corresponding ratio of mean square radii of gyration), by means of polymerization parameters, size exclusion chromatography, viscosity measurement, and amount of total unsaturation. The calculation based on our experimental data shows the following, in radical polymerization of ethylene. (1) With reaction pressure and temperature varied, the degree of long-chain branching was 0.5 to 3.7 per 1000 carbons. (2) As for the rate constant for long-chain branching, the activation energy Etrp- Epand the activation volume Δ Vtrp* - ΔVp* were 4.1 kcal/mol and 20 cc/mol, respectively. (3) The value of the exponent α, which is considered to represent the type of branching, was independent of reaction pressure and decreased with an increase of reaction temperature, and it was between 0.9 to 1.5, centering around 1.1. The validity of these values in (1), (2), and (3) and the type of branching are discussed.