The present invention relates to modafinil or derivatives thereof as a medicine for the treatment of vascular diseases or KCa3.1 channel (Ca activated K channel) mediated diseases and a novel use of the same. More specifically, the present invention relates to a pharmaceutical composition for the prevention or treatment of vascular diseases or KCa3.1 channel-mediated diseases comprising modafinil or a derivative of modafinil, or pharmaceutically acceptable salts thereof which relax blood vessels and inhibit KCa3.1 channel currents by increasing intracellular cAMP, a method for treating vascular diseases or KCa3.1 channel-mediated diseases using the composition and a health functional food composition for the prevention or improvement of vascular diseases or the KCa3.1 channel-mediated diseases comprising modafinil or a modafinil derivative compound, or sitologically acceptable salts thereof.