To elucidate the mechanism of brominated natural rubber (BNR),eight BNR samples with different bromine content were prepared from latex in different bromination time,and the microstructures were characterized by Fourier transform infrared spectroscopy (FTIR) and 1H-NMR spectroscopy,respectively.The hardness of BNR increased and its nature transformed from elastomer to resin with the increase of bromine content.Unlike chlorinated natural rubber (CNR),FTIR showed that there were no carbonyl groups on the molecular chains of BNR.1H-NMR spectroscopy revealed that the reaction activity of bromine and the secondary hydrogen atom of BNR were much higher than those of the primary one.The brominated substitution took place in the hydrogen atom of CH3 and CH2 groups firstly,then in the late period of bromination the bond of C=C was transferred to the saturated bond of C-C due to the Markovnikov addition of hydrogen bromide.Based on these findings,the mechanism of BNR from latex could be deduced as a free radical reaction and the detailed bromination process was presented.