The term monster ’fetus acardius’ is the one of the monozygotic twin who is greatly malformed, reduced and has atrophied or rudimentary body component but no heart or very imperfect one, mainly due to abnormal anastomosis of umbilical vessel in the common placenta between normal and malformed twin. Up today, many cases are reported as the four types, acardius ancephalus, acardius acephalus, acardius acormus and acardius amorphus. Here, we have a good opportunity to study one case of fetus acardius at the Department of Pathology, Catholic Medical College.