Based on a pot experiment conducted with seven upland soils collected from Huhei and Hunan Provinces,a research was made on the dynamics of hot-water soluble boron(HWSB),Mannitol-B and NH₂OH·HCl-B during rape growing periods.The results showed that from before rape transplanting to flower-bud appearing,then to fully blooming,the content of HWSB in the treatment without boron had a tendency of constant increase,but that in the treatment with boron went up slightly after it had decreased obviously.And the content of Mannitol-B tended to keep increasing in both the treatments.At the same time,the content of NH₂OH·HCl-B tended to be stable.The relationships among the three kinds of soil boron were that Mannitol-B and HWSB could transform with each other under the effect of environmental factors;NH₂OH·HCl-B and HWSB were fundamentally the same boron fraction,which was due to that the soils were acidified and the Mn oxyhydroxides were reduced strongly after the several planting experiments.For the same reason,relationship between Mannitol-B and NH₂OH·HCl-B in the experimental soils weakened compared to that in the primary soils.