A new methodology is proposed to quantify long-chain branching (LCB) molar fraction in polypropylene (PP) systems. Gel permeation chromatography and small-amplitude oscillatory shear were employed to quantify LCB molar fraction and its influence on rheology in PP. Introduction of an increasing amount of coupling agent during extrusion leads to the formation of a proportional level of LCB molar fraction in the model PP investigated. The dependency of zero-shear viscosity (eta(0)) on the weight-average molecular weight allows for a reliable estimation of eta(0) of LCB component in PP. Logarithmic mixing rule has been applied to obtain LCB molar fraction in each LCB-containing PP system. A quantitative assessment on how the LCB molar fraction influences PP rheological behavior is proposed.