The effects of nootropic drug Semax on the neuronal network of the brain were studied by the resting state functional magnetic-resonance imaging (resting state fMRI). The study was carried out on two groups of healthy volunteers (11 men and 13 women aged 43.9±9.5 years). Resting state fMRI was carried out 3 times: directly before and 5 and 20 min after intranasal 1% Semax (14 subjects) or placebo (10 subjects). The topography of the resting state default mode network was studied. A greater volume of the default mode network rostral (medial frontal cortex) subcomponent was detected in the Semax group in comparison with controls. Resting state fMRI confirmed Semax effects on the neuronal network of the brain and demonstrated topography of these effects.