AbstractThe Sendai virus vector has received a lot of attention due to its broad tropism for mammalian cells. As a result of efforts for genetic studies based on a mutant virus, we can now express more than 10 genes of up to 13.5 kilo nucleotides in a single vector with high protein expression efficiency. To prove this benefit, we examined the efficacy of the novel ribonucleic acid (RNA) virus vector harboring the human iduronate‐2‐sulfatase (IDS) gene with 1,653 base pairs, a causative gene for mucopolysaccharidosis type II, also known as a disorder of lysosomal storage disorders. As expected, this novel RNA vector with the humanIDSgene exhibited its marked expression as determined by the expression of enhanced green fluorescent protein and IDS enzyme activity. While these cells exhibited a normal growth rate, the BHK‐21 transformant cells stably expressing the humanIDSgene persistently generated an active human IDS enzyme extracellularly. The human IDS protein produced failed to be incorporated into the lysosome when cells were pretreated with mannose‐6‐phosphate, demonstrating that this human IDS enzyme has potential for therapeutic use by cross‐correction. These results suggest that our novel RNA vector may be applicable for further clinical settings.