In modern systems-on-chip (SOC) technology analog modules are costly to design. This paper studies an optimal realization of switched-capacitor (SC) circuit given a transfer function (TF) in the z-domain. Among the multiple possibilities of capacitance assignments, the proposed method is more controllable in arriving at a desirable SC realization. The underlying technique applies a symbolic method to derive a cancellation-free symbolic representation for a given SC circuit topology, then uses the automatically generated symbolic coefficient expressions to synthesize a set of numerical capacitance values suitable for physical implementation. Examples demonstrate the effectiveness of the proposal.