氟只有一种稳定的天然同位素，即包含有10个中子的19F。该原子具有较高的磁旋比，原子核能级受磁场的影响比较明显。又由于氟仅有一种稳定同位素，它经常用于核磁共振 。目前一共合成了质量数从14到31的17种氟的放射性同位素，其中半衰期为109.77分钟的18F最为稳定。其它同位素的半衰期都小于70秒，大多数都小于半秒钟。同位素与的衰变方式为正电子发射，更轻的同位素的衰变方式为电子俘获，更重的同位素的衰变方式为β衰变或中子发射。目前已知氟有一种亚稳态异构体，其半衰期为234纳秒。
Fluorine has only one stable natural isotope, 19F, which contains 10 neutrons. This atom has a high magnetic rotation ratio, and its nuclear energy level is obviously affected by the magnetic field. Because fluorine has only one stable isotope, it is often used in NMR. At present, 17 kinds of radioisotopes with mass number from 14 to 31 have been synthesized, of which 18F with half-life of 109.77 minutes is the most stable. Other isotopes have half lives of less than 70 seconds, most of which are less than half a second. The decay mode of isotopes and is positron emission, the decay mode of lighter isotopes is electron capture, and the decay mode of heavier isotopes is β decay or neutron emission. It is known that fluorine has a metastable isomer with a half-life of 234 nanoseconds.