Carbon nanotubes (CNTs) are very promising for use in various areas of human activity, including medicine, but they can have a negative effect on the body, in particular on the nervous system. CNTs in large doses in animal experiments often cause anxiety and depressive disorders. The effect of low doses of CNTs on the behavior of animals has been little studied. In the present work, we studied behavioral parameters in tests for anxiety in rats, which were intranasally injected daily for 4 days with a suspension of single-walled carbon nanotubes (SWCNTs) in small doses, 5.2 µg/kg or 52 µg/kg. It turned out that both doses of SWCNTs unidirectionally changed the following indicators of behavior in rats: in the open field test exploratory activity (rears) decreased; in the light–dark box test the latency of entering to the dark box and peeping out of the dark box and are increased; in the elevated plus maze test (EPM) behavior in the open arm was activated. However, if a dose of 5.2 µg/kg induced the rat behavior with signs of agitation (increased exploratory motor activity in the light–dark box and EPM tests, and motor activity with frequent visits to different boxes or arms and exploratory activity in the light–dark box and EPM tests), then a dose of 52 µg/kg, on the contrary, inhibited a number of behavioral responses, which was expressed in increased anxiety (increased the freezing in the open field and EPM) and in increased the latency of entry into the closed arm of the EPM. It is assumed that SWCNTs in small doses, when injected intranasally into the brain of rats, can dose-dependently disrupt the structural and functional state of nervous tissue cells and/or cause neuroinflammation in the structures involved in the mechanisms of anxiety and related conditions, as a result, the behavior of rats in tests for anxiety also changes in a dose-dependent manner. [ABSTRACT FROM AUTHOR]