Abstract: Application of animal cloning is limited with especially low efficiency and birth defect cloned offspring.This is because molecular mechanism underlying animal cloning is not well known.For better understanding of current progress in this field,we gathered reports on molecular ways affecting the success of animal cloning,such as nuclear-cytoplasm interaction,epigenetic reprogramming,mitochondrial fate,telomere changing and X chromosome inactivation,etc.It looks as if the application of some new techniques such as bio-CMOS chip would help resolving the problems.