Discovery of RNA interference (RNAi)-mediated specific gene silencing has raised hope for cancer therapy. Unfortunately, the execution of RNAi by delivering small-interfering RNA (siRNA) or small hairpin RNA (shRNA) remains a prime challenge. A methodical evaluation of cationic polymers in RNAi-based cancer studies may offer a promising solution to this problem. In this chapter, we report the methodologies for comprehensive characterization of a biodegradable polymeric system for sh/siRNA delivery in cancer studies. The chapter will describe synthesis, characterization, and optimization of biodegradable poly (β-amino ester) for sh/siRNA delivery. The protocols are provided for shRNA and siRNA complex preparation, stability and morphology study. Also, detailed methods are provided for the intracellular tracking and transfection of sh/siRNA using polymeric carrier. In addition, step-wise information is provided for the in vitro silencing of oncoprotein to study important cancer properties, including proliferation, malignancy, and metastasis of cancer cells.