D−Amino acids are the sterically antipodes of L−amino acids, which have been recognized as the only homochiral protein amino acids until recently, but actually exist in nature. Free amino acids : D−Asp, D−Ser, D−Ala etc. have been found in many organisms. D−Amino acids form as building blocks in proteins during epimerization. Many teachers and researchers might still have a perspective that D−amino acids do not exist in proteins and tissues of organisms. Since so many studies have shown the perspective not right, the teachers' knowledge and the textbooks' description have to change for the students of the next generation. This research also exemplifies several teaching materials for understanding of D−amino acids.