A case of paternity was referred to the Medical-Legal Directorate( MLD)/ Baghdad in August 2011 .The family who were concerned was the  Father (41 years old ) ,mother (23 years old) and 2 sons non identical twin (1.5year old) . Paternity test includes Conventional Blood Group Markers, DNA and Y chromosome STR Typing were investigated . The DNA and Y chromosome STR Typing were tested  for the referred trios father and twins first , the results revealed an absolute exclusion of fatherhood relationship to both . , surprisingly the Y Chromosomeprofiles  revealed obviously that the two non identical twins were from different fathers or paternal descent. Maternity test was ought to be examined  for the assumed mother to rule out the possibility of switch of both babies in the hospital during their delivery and to prove their brotherhood relationship from mother side. The mother was referred and maternity was confirmed later using DNA Typing . Combined Maternity Index (CPI) was calculated for twins ,The probability of Maternity were 99.98% and 99.95% for the1st and 2nd twin respectively. Key words : hetero paternal Superfecundation ,Non Identical twin,DNA Typing ,Y Chromosome STR Polymorphysim