The isotope ratio of molecules is a powerful tool for investigating the origin of solar system materials and for revealing the possible chemical link between the solar system and the interstellar medium. More and precise isotope ratios have been quantified through spacecraft missions to various solar system bodies and the high sensitivity ALMA observations of molecular isotopologues in star and planet forming regions.  Furthermore, the development of numerical modeling considering detailed gas-phase chemical networks with grain surface reactions, has improved our understanding of isotope chemistry. In this talk, I will present observational and theoretical progress of isotope ratios, especially the nitrogen and carbon isotope ratios, in the protoplanetary disks.