Compounds including 5-(Heterocyclyl)alkyl-N-(arylsulfonyl)indole, their derivatives, their stereoisomers, their pharmaceutically acceptable salts and pharmaceutically acceptable compositions containing them and a process for the preparation of these compounds, their derivatives, their stereoisomers, their pharmaceutically acceptable salts and pharmaceutically acceptable compositions containing them. These compounds are useful in the treatment of various disorders that are related to 5-HT6 receptor functions. Specifically, the compounds of this invention are also useful in the treatment of various CNS disorders, hematological disorders, eating disorders, diseases associated with pain, respiratory diseases, genito-urological disorders, cardiovascular diseases and cancer.