Chitosan (CS) combined with poly-L-arginine (PLA) was formulated and evaluated for its performance to deliver siRNA to HeLa cells expressing enhanced green fluorescent protein (EGFP). Compared with the formulations using single polymer in which the polyplexes were completely formed at the weight ratio of >20 : 1 for CS/siRNA or 1 : 1 for PLA/siRNA, the combination of CS and PLA could reduce the amounts of the polymers required for the complete complexation with siRNA, thereby forming positively charged, nanosized polyplex at the weight ratio of CS/PLA/siRNA of 5 : 0.5: 1. In addition, while the transfection efficiency of CS/siRNA and PLA/siRNA was very low at physiological pH (7.4), CS/PLA/siRNA at the optimal weight ratio of 5 : 0.5 : 1 satisfactorily silenced the endogenous EGFP gene at pH 7.4 as well as at pH 6.4 without the deterrent effect from serum. The combined polymers could protect siRNA from RNase degradation over a period of at least 6 h. Furthermore, MTT assay results demonstrated that CS/PLA/siRNA complexes showed acceptably low cytotoxicity with 75% cell viability. Therefore, CS combined with PLA is easy to prepare, safe, and promising for use as an efficient siRNA delivery vehicle.