Abstract: In order to determine the diffusivity of vitamin B6,a real-time laser holographic interferometer was employed.The diffusion coefficients of vitamin B6 in aqueous solution and in biologic brine were obtained at 298.15K respectively.The results show that,the diffusion coefficient of vitamin B6 in aqueous solution decreases unilaterally with the concentration of vitamin B6,but in biologic brine the diffusion coefficient increases up to a maximum and then decreases remarkably with the concentration of vitamin B6,it is mainly due to the special self-structure of vitamin B6 and the effect of different interaction existing in different solution.The above characteristic hasn't been reported so far in literature.Relative explanation and discuss were given in this paper according to the integrated effect of H-bond action,interaction between particles,ion intensity and friction resistance between solute and solvent,etc.The results are important to the medical field.