Abstract: The present invention relates to novel substituted 3-(arylsulfonyl)pyrazolo[1,5-a]pyrimidines of general formula 1 pharmaceutically acceptable salts and/or hydrates, to novel serotonin 5-HT6 receptor antagonists, to novel drug substances, pharmaceutical compositions, medicaments and methods for their preparation and use for treatment and prophylaxis of pathological states and diseases of CNS, pathogenesis of which is associated with disturbance of serotonin 5-HT6 receptor activation. In compounds of general formula 1 Ar represents optionally substituted aryl or heterocyclyl; R1, R2 and R3 independently of each other represent hydrogen, C1-C3 alkyl or phenyl; R4 represents hydrogen, optionally substituted C1-C5 alkyl, substituted hydroxyl group or substituted sulfanyl group.