Naturally occurring praseodymium (59Pr) is composed of one stable isotope, 141Pr.
Thirty-eight radioisotopes have been characterized with the most stable being 143Pr, with a half-life of 13.57 days and 142Pr, with a half-life of 19.12 hours.
The isotopes of praseodymium range in atomic weight from 120.955 u (121Pr) to 158.955 u (159Pr).
The primary decay mode before the stable isotope, 141Pr, is electron capture and the mode after is beta decay.
The primary decay products before 141Pr are element 58 (cerium) isotopes and the primary products after are element 60 (neodymium) isotopes.