In many cardiovascular diseases, differences between women and men have been well described in epidemiology, pathophysiology, clinical manifestations, treatment efficacy, and outcomes, and have attracted attention as an aspect of personalized medicine. Recently, the use of induced pluripotent stem cells (iPS) cells to reflect individual differences in the drug discovery and the toxicological assay has been attracting attention, but a screening assay system for human cells to evaluate sex differences has not yet been established. Thus, we here propose to develop an in vitro system using iPS cell lines derived from a pair of dizygotic twins. We report the progress of three pairs of clones selected for future sex-differences analysis; no sex differences were observed in the expression of the three germline differentiation markers. As a next step, we plan to examine sex differences in gene expression in twin pairs of undifferentiated and differentiated cardiomyocytes to obtain data that will form the basis for future functional analysis of iPS cell-derived cardiomyocytes, including cardiotoxicity assessment.