The sooting behavior in the laminar premixed flames of acetylene, ethylene, and ethane was studied both experimentally and computationally to explore the effect of fuel structure on nascent soot formation. The particle size distributions were measured using an orifice sampling technique coupled with a scanning mobility particle sizer. The particle morphology was examined using a nanometer aerosol sampler coupled with a transmission electron microscope. Numerical simulations of soot volume fraction and gas species concentrations were carried out to analyze the experimental observations. At the same C/O ratio of 0.667 and maximum temperature of around 1790 K, the ethane flame shows the highest rates of nucleation and mass growth among the three C2 flames, while much fewer and smaller particles are observed in the acetylene flame than those in the ethylene and ethane flames. Simulation results indicate soot volume fraction is very sensitive to the nucleation rate, while surface reactions only play a role at higher flame heights. All three flames share reaction paths similar to benzene, whereas some oxidation reactions are more dominant in the acetylene flame due to the lower equivalence ratio that inhibits soot formation.