Induced Pluripotent Stem Cells (iPSCs) are Embryonic Stem Cell (ESC) - like cells which are reprogrammed directly from somatic cells, by ectopic expression of the reprogramming factors (RFs), including Oct4, Sox2, Klf4, and c-Myc. iPSC technology hold great potential in stem cell therapy by generating patient-specific pluripotent cells and by circumventing the ethical issue of ESC derivation from human embryos. However, the introduction of RFs to cells by viral or other vectors raised concerns over tumorigenicity due to genomic DNA integration. iPSCs could be induced by reprogramming proteins (piPSC) linked to cell penetrating peptides (CPPs) such as poly-arginines. This approach bypasses genomic alteration to the cells. However the piPSC induction efficiency was extremely low and the optimal protein transduction conditions were not well established. We aimed to evaluate the reprogramming potency of recombinant proteins fused to the CPPs of human immunodeficiency virus transactivator of transcription (HIV TAT). To this end, we expressed and purified various recombinant Klf4, conducted in vitro protein functionality tests, and compared their reprogramming potency using a combined protein/retroviral Oct4, Sox2, and c-Myc induction assay. We found that TAT linked Klf4 proteins can effectively induce iPSC colony formation in 2 to 4 weeks from fibroblasts. Using the combined protein/retroviral induction assay, we further evaluated key parameters in piPSC induction, including protein transduction dosage, frequency, and transduction cycles. We found that a 4-cycle-transduction of recombinant Klf4 is sufficient for effective iPSC induction. Our data demonstrated that TAT-fused Klf4 can effectively replace viral Klf4 in reprogramming fibroblasts, and provided a valuable strategy to evaluate the potency and transduction conditions for recombinant RFs in order to improve the piPSC induction efficiency.