Inactivation of tumor suppressor genes is a key factor in cancer regulation. N-myc downstream regulated gene 1 (NDRG1) is a tumor suppressor gene well known to be involved in carcinogenesis of numerous cancer types. The present study was designed to investigate the role of NDRG1 in human ovarian cancer, using SKOV-3 and SW626 (moderately and well differentiated cancer cells, respectively). Our results revealed that over-expressed NDRG1 significantly up-regulated the differentiation marker p21, in the ovarian cancer cell lines. This regulation led to decrease in cell viability and DNA synthesis rates in SW626 cells (83% and 89.5%, respectively). However, no effect on viability or on DNA synthesis was observed in SKOV-3 NDRG1-transfected cells. These findings prove that NDRG1 is indubitably functional in human ovarian cancer cells, as it up-regulated p21 expression. Nevertheless, this regulation showed differential effect on cell viability and DNA formation thus promoting the perception that downstream regulation of p21 could be inefficient in some cancer cells, a concept that needs to be further explored in order to understand its disability to play as regulator of cell cycle progression.