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Expression of chloride channel 1 ( CLCN1/ClC-1 ) in skeletal muscle is driven by alternative splicing, a process regulated in part by RNA-binding protein families MBNL and CELF. Aberrant splicing of CLCN1 produces many mRNAs, which were translated into inactive proteins, resulting in myotonia in myotonic dystrophy (DM), a genetic disorder caused by the expansion of a CTG or CCTG repeat. This increase in abnormal splicing variants containing exons 6B, 7A or the insertion of a TAG stop codon just before exon 7 leads to a decrease in expression of the normal splice pattern. The majority of studies examining splicing in CLCN1 have been performed using mouse Clcn1 , as have investigations into the activation and suppression of normal splicing variant expression by MBNL1-3 and CELF3-6 , respectively. In contrast, examinations of human CLCN1 have been less common due to the greater complexity of splicing patterns. Here, we constructed a minigene containing CLCN1 exons 5-7 and established a novel assay system to quantify the expression of the normal splicing variant of CLCN1 using real-time RT-PCR. Antisense oligonucleotides could promote normal CLCN1 alternative splicing but the effective sequence was different from that of Clcn1 . This result differs from previous reports using Clcn1 , highlighting the effect of differences in splicing patterns between mice and humans.