Currently, neutron capture therapy is a promising cancer treatment. This method is based on the reaction of thermal neutron capture by some nonradioactive elements (e.g., Gd¹⁵⁷), which results in the subsequent emission of electrons and gamma rays. An effective instrument for delivering gadolinium into tumor tissue are "rigid" nanostructures (NSs) based on double-stranded DNA complexes with gadolinium (NS-Gd). The local concentration of Gd in these nanostructures may reach 40%. To optimize the process of neutron capture therapy, it is very important to investigate possible mechanisms of the penetration of NS-Gd particles into tumor cells. In this work, the dynamics of interaction between NS-Gd and cultivated Chinese hamster ovary cells (CHO) was studied by confocal and electron microscopy. NS-Gd were shown to be able to enter CHO cells. This process started after about 1 h of incubation. After 6 h, NS-Gd particles were detected in almost all cells. A further increase in the incubation time did not lead to significant changes in cell morphology, although the amount of NS-Gd inside cells continued to increase. The plasma membranes of the cells remained intact. Once entering the cells, NS-Gd particles remained there for a long time. The data show that NS-Gd has relatively low toxicity and suggest that the presence of NS-Gd in tumor cells does not prevent their division. The data are important for improving the efficiency of the method of neutron-capture therapy.