This work presents an in situ experimental investigation of the shear-induced coalescence mechanism in low concentration polymer blends (1%-10%). An original sizing method based on small-angle light scattering and optical microscopy were used to determine the evolution of the drop size distributions as a function of time. In order to study the pure coalescence mechanisms, measurements were conducted according to a specific flow protocol. The influences of the shear rate, initial morphology, concentration of the polymer blend and phase inversion on the coalescence kinetics were investigated. The investigated. blends are mixtures of polydimethylsiloxane and polyisobutene. The amount of Strain, the step-down rate ratio and the concentration squared are identified as relevant parameters to describe the coalescence kinetics. The dependence of the steady state drop sizes on the applied shear rate is well described by a coalescence model considering partially mobile interfaces.