The sol-gel transition of tetrafunctional polymers with mutual reactive end-groups was investigated by analyzing the dynamics of probe particles via dynamic light scattering. The dynamics of probe particles was exclusively observed by matching the refractive index of the solvent and the polymers. The sol-gel transition point, decreasing of sol fraction and increasing of gel fraction with the reaction, the onset of formation of closed structure inside branched polymer clusters, and a piece of evidence for the decrease of the local 1.13+0.06 viscosity in postgel regime were observed via the dynamics of probe particles. In addition, a scaling relationship eta(eff) similar to epsilon(-1.13 +/- 0.06) was found in a wide range of cross-linking conversion (p) before the gel point, where eta(eff) is the effective viscosity estimated from probe particles' dynamics and epsilon = lp- p(c)l/p(c), is the relative distance from the sol-gel transition point (p(c) is the cross-linking conversion at gel point).