The effect of short-chain branching (SCB) on the persistence length lp of polyethylene (PE) was studied using small-angle neutron scattering (SANS). In thermodynamically good solvents, lp can be measured directly from the scattering vector qtr at the crossover from good solvent mass-fractal scaling to the rodlike persistent scaling, using the unified equation described in the text. The method was used to study lp of both linear and branched PE in deuterated p-xylene, which is a good solvent for PE at 125 °C. The results indicate an increase in lp of the backbone chain with increasing SCB content, independently measured using Fourier transform infrared spectroscopy (FTIR). These results corroborate the behavior previously reported in Monte Carlo simulations of short-chain branched polymers. A functional relationship for lp in terms of the number of SCBs is proposed.