Alternative splicing of pre-mRNAs greatly contributes to diversity in products generated from a single gene. However, the underlying regulatory mechanisms are poorly understood. In the present study, we describe evolutionarily conserved intra-intronic and inter-intronic RNA secondary structures. Mutation experiments revealed that intra-intronic RNA secondary structure causes steric hindrance to enforce mutual splicing exclusivity, while inter-intronic RNA pairing largely functions through a looped-out mechanism. Moreover, mutually exclusive splicing may be regulated by RNA pairing competition between intra- and inter-introns. Importantly, the resulting dynamic RNA architecture largely controls mutually exclusive splicing, although cis-acting regulatory sequences may fine-tune this process. Our results emphasize the importance of dynamic RNA architecture in alternative splicing.