RNA interference (RNAi) is a sequence-specific mechanism to control the expression of target genes. This technique has proven potentials both in vivo and in vitro. The main hurdle for using RNAi-based therapy is the effective delivery of RNAi-based drugs to the target cells or tissues in vivo. The aspects of off-target effects, delivery methods, induction of immune response and dose determination for delivery should, however, be considered carefully. If these challenges associated with siRNA can be met, then the potentials of RNAi could be exploited to the full for the development of therapeutic tools and drugs.