This manuscript describes an investigation of the role of speciation of 137Cs in two soils from forests contaminated 40 years ago from atmospheric weapon testing fallout. Sequential extraction of 137Cs, i.e., readily exchangeable, bound to microbial biomass, bound to Fe-Mn oxides, bound to organic matter, persistently bound and residual fractions were determined. The results show that only trace amounts were bound to the exchangeable, microbial biomass, and Fe-Mn oxides fractions. Most 137Cs was bound to the persistent (52–62%) and residual (28–41%) fraction. Despite the high organic matter contents (46 and 83%) in the soils, only minor amounts were bound to organic matter (4–10%). Only limited fraction of 137Cs bound to labile and moderately labile forms of soil, which is consistent with those of organic C. The results suggest that labile form of 137Cs is mostly transferred to the stable and resistant fractions after long-term deposition of fallout. It supports previous findings that 137Cs recycles through the soil and plant systems and will not be easily removed from a perhumid forest ecosystem.