A series of 8-phenyl-isoquinoline derivatives (I) exhibit high binding affinity to 5-HT7 receptor (5-HT7R) and demonstrate potent antinociceptive activity in two animal models for Irritable Bowel Syndrome (IBS) by intraperitoneal injection (i.p.) or by oral administration (p.o.). These 5-HT7 receptor antagonists are a new class of therapeutic agents for the treatment of IBS.