Poly(ADP-ribosyl)ation is a modification of nuclear proteins that regulates DNA replication, repair and transcription. In order to investigate the biological effects of degradation of poly(ADP-ribose), knockdown of the poly(ADP-ribose) glycohydrolase (PARG) gene was performed by introducing a short interfering RNA (siRNA)-pool into HeLa S3 cells. Notably, poly(ADP-ribosyl)ated proteins did not accumulate in the cells. Western blotting, quantitative RT-PCR analysis and a transient transfection assay revealed that poly(ADP-ribose) polymerase 1 (PARP1) gene/protein expression and its promoter activity were reduced in the PARG knockdown cells. These results suggest that the amount of poly(ADP-ribose) in a cell is regulated under the control of PARP1/PARG gene expression balance. Furthermore, in this study, we showed that PARG-siRNA enhanced cell death induced by staurosporine (STS). Thus, we propose a PARG-siRNA utilizing gene-therapy for cancer treatment.