The present invention provides methods for improving the efficiency of inducing pluripotent stem cells, as well as vectors and compositions for use therein. In the induction of pluripotent stem cells which contains the step of introducing a vector that contains the KLF gene, OCT gene, and SOX gene in this order, the efficiency of pluripotent stem cell induction was successfully increased significantly by further introducing a vector that contains the KLF gene but not the OCT gene and the SOX gene. The methods of the present invention have an excellent feature in that they allow efficient induction of pluripotent stem cells under a temperature condition closer to the physiological environment, and prompt vector removal after the pluripotent stem cell induction. The present invention enables more efficient induction of pluripotent stem cells.
