A systematic literature search and a comparative study were conducted to investigate the evolution of the levels of evidence and strength of recommendations in medical research. Fifty systems were included from 1979 to 2007, and 11 of these, which came from five states or international organizations, were selected and divided into three stages according to their characteristics, sphere of influence and application fields. Ideas about levels of evidence and strength of recommendations are becoming mature in medical research. The challenge for the future is how to introduce evidence-based principles and develop the corresponding levels of evidence and strength of recommendations in the fields of management, education, basic medical sciences, economics, sociology and legal research.