The objective of this study was to assess cytotoxicity of engineered MnO nanoparticles by quantifying the reactive oxygen species (ROS) related genes (glutathione S-transferase (GST) and catalase) using real time-polymerase chain reaction (RT-PCR) and molecular beacon (MB) technologies. Monodisperse MnO nanoparticles of 14 nm in size were synthesized by the encapsulation of polyethyleneglycol (PEG)-phospholipid shell around the MnO core to endow high water-dispersibility and biocompatibility. In vitro cytotoxicity was evaluated at different concentrations (10, 50 and 100 mu g/ml) and incubation times (12, 24 and 48 h) with human cancer cell lines (glioblastoma, lung adenocarcinoma and neuroblastoma cells). Both genetic and cellular cytotoxic screening methods produced consistent results, showing that GST and catalase ROS gene expression was maximized in 24 h incubation at 100 mu g/ml concentration of MnO nanoparticles for each cell line. However, the cytotoxicity effect of the PEG-phospholipid coated MnO nanoparticle was not significant compared with control experiments, demonstrating its high potential in the applications of nanomedicines for a diagnostic and therapeutic tool.