Abstract Cell fusion is one approach that has been used to demonstrate nuclear reprogramming of somatic cells to a pluripotent-like state and is a useful tool for screening factors involved in reprogramming. Recent cell fusion studies reported that the overexpression of Nanog and SalI could improve the efficiency of reprogramming, whereas AID was shown to be essential for DNA demethylation and initiation of reprogramming. The aim of this study was to investigate factors affecting the reprogramming efficiency following cell fusion. We conducted fusions of mouse embryonic stem cells (ESCs) with somatic cells carrying a GFP transgene under control of the Oct4 promoter (Oct4-GFP), which is normally repressed in nonpluripotent cells. The effect of somatic cell type on the reprogramming efficiency was investigated using Oct4-GFP expression as an indicator. Different somatic cell types were tested including mesenchymal stem cells (MSCs), adipose tissue-derived cells (ADCs), neural stem cells (NSCs), and these were compared with the mouse embryonic fibroblast (mEF) standard.