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Nanoparticles, as nonviral vectors, have attracted attention for their ability in gene delivery and are currently considered to be prospective future vectors for biological and biomedical application . We prepared organically modified cationic silica nanoparticles toward the high performance nonviral vector. It is to be noted that the complexes of DNA and nanoparticles are regarded as a simple model of chromatin. Furthermore, it is reported that the transcription activity of DNA is preserved after complexing with small nanoparticles, where the manner of complex formation is strongly dependent on the size of the nanoparticles in vitro. On the other hand, it is confirmed that transcription is completely inhibited in the compact globule state of giant DNA induced by polyamines and related polycations. In the present study, we transfected the nonvel type nanoparticles into mammalican cells. It has been found that the nanoparticles are very effectively taken up by both cytoplasm and nucleus of cells according to the observation by fluorescence confocal microscopy. In addition, we have also demonstrated that the nanoparticles are non-toxic for cell. Furthermore, it is particularly important that almost 100% HeLa cells were observed incorporating nanoparticles which suggests that treatment of cells with these nanoparticles can secure uniform and total (in terms of cell population) filling of cells with the nanoparticles. The observed time dependence and size effect in the process of nanoparticles uptake by cells suggests that the scenario of nanoparticles uptake by cells can be programmed by varying size and time parameters. From all these findings, we consider that the nanoparticles may be used as a highly efficient and safe gene transfer vectors. As future work, we will investigate if the cationic silica nanoparticles can efficiently bind and transfect plasmid DNA. On the other hand, it is also interesting to study whether nanoparticles can make any change of the higher-- order structure of genomic DNA, and hence the activity of transcription.