RNA interference methodology suppresses specific gene expression, thus mimicking loss-of-function mutation and enabling in vitro and in vivo gene function analysis. Lipofectamine RNAiMAX, a new transfection reagent, has been confirmed high efficiency in delivering small interfering RNA (siRNA) into mesenchymal stem cells and neural stem cells. In this study, we used three transfection reagents (Lipofectamine RNAiMAX, Oligofectamine and Lipofectamine 2000) to deliver siRNA into human embryonic stem (hES) cells and compared the silencing efficiency of enhanced green fluorescent protein transgene and Oct4, a key regulator of pluripotency. As a result, siRNA can be delivered into hES cells more efficiently by Lipofectamine RNAiMAX compared with the other two transfection reagents and high efficient knockdown of target genes was obtained by Lipofectamine RNAiMAX even at a low concentration of siRNA. Quantitative real-time PCR showed approximately 90% knockdown of Oct4 transcript with cognate Oct4 siRNA transfection by Lipofectamine RNAiMAX compared to control siRNA. These results demonstrated that Lipofectamine RNAiMAX is an efficient and excellent transfection reagent for delivering siRNA into hES cells.