NOVEL PROCESS FOR PRODUCING RAMOSETRON OR ITS SALT

[PROBLEMS] To provide a novel process for producing ramosetron or its salt that is useful as a pharmaceutical, especially as a therapeutic and/or preventive agent for digestive symptoms caused by administration of an anti-malignant tumor agent, diarrheal-type irritable bowel syndrome, diarrheal symptoms of irritable bowel syndrome, etc. [MEANS FOR SOLVING PROBLEMS] Ramosetron or its salt can be produced by reacting any of compounds of the formula: (I) [wherein X is a halogen] or a salt thereof with 1-methyl-1H-indole in the presence of a Lewis acid selected from the group consisting of lower-alkylaluminum dihalides, di-lower-alkylaluminum halides, tri-lower-alkylaluminums and lower-alkylaluminum sesquihalides.