Microcatheters for neuroendovascular procedure especially for embolization of aneurysms are essential tools. Each catheter has it's own property for use. However there is very little literature about the character and mechanism of microcatheters. With steam shaping, they are often deformed and shortened. We herein present technical problems associated with the shaping of microcatheters. We have to understand the potential risk of complications related to microcatheters.